2021 JAMB Chemistry Past Questions and Answers

Questions

1. 1.

   Soaps clean surfaces on the principle based on?

   1. A.viscosity
   2. B.floatation
   3. C.elasticity
   4. D.surface tension

   Show answer

   Answer: D. surface tension

   AI explanation

   Analysis of the Question

   The question asks for the underlying physical principle that allows soap to function as a cleaning agent. To answer this, we need to understand how soap molecules interact with water and dirt (grease/oil).

   Explanation of the Concept

   Soap molecules are amphiphilic, meaning they have two distinct parts:

   1. Hydrophilic head: This part is water-loving and dissolves in water.
   2. Hydrophobic tail: This part is water-hating (lipophilic) and dissolves in grease or oil.

   When soap is added to water, it significantly reduces the surface tension of the water. Surface tension is the cohesive force that makes the surface of a liquid act like a stretched elastic membrane. By lowering this tension, the water can spread out more easily, penetrate fabrics, and "wet" the surface better.

   Furthermore, the soap molecules surround the grease particles, forming structures called micelles. The hydrophobic tails bury themselves in the grease, while the hydrophilic heads point outward into the water. This process emulsifies the grease, allowing it to be lifted off the surface and washed away.

   Step-by-Step Solution

   1. Identify the role of soap: Soap acts as a surfactant (surface-active agent).
   2. Analyze the options: • Viscosity: This is a measure of a fluid's resistance to flow. While soap changes the properties of water, cleaning is not primarily about flow resistance. • Floatation: This is a process used in metallurgy to separate ores, not the primary principle of cleaning. • Elasticity: This refers to the ability of a material to return to its original shape after deformation, which is unrelated to the chemical cleaning action of soap. • Surface Tension: By reducing the surface tension of water, soap allows the water to penetrate dirt and grease, effectively lifting it from the surface.
   3. Conclusion: The reduction of surface tension is the fundamental physical change that enables soap to clean surfaces.

   Identifying the Answer

   Exam Tip

   Whenever you see a question about soap, detergents, or surfactants in Chemistry, look for keywords like "surface tension," "emulsification," or "micelle formation." These are the three pillars of how soap works!

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2. 2.

   The gas which causes global warming is?

   1. A.O$_{2}$
   2. B.CO$_{2}$
   3. C.N$_{2}$
   4. D.He

   Show answer

   Answer: B. CO$_{2}$

   AI explanation

   1. Analyze the question

   The question asks us to identify which of the listed gases is a primary contributor to global warming. Global warming is the long-term heating of Earth's climate system observed since the pre-industrial period due to human activities, primarily fossil fuel burning, which increases heat-trapping greenhouse gas levels in Earth's atmosphere.

   2. Explain the concept

   Global warming is caused by the Greenhouse Effect. Certain gases in the atmosphere, known as greenhouse gases, allow sunlight to pass through the atmosphere to warm the Earth's surface, but they prevent the heat (infrared radiation) emitted from the surface from escaping back into space. This trapped heat warms the planet.

   • O$_{2}$ (Oxygen): Makes up about 21% of our atmosphere and is essential for respiration; it is not a greenhouse gas.
   • CO$_{2}$ (Carbon dioxide): Produced by the combustion of fossil fuels (like petrol, coal, and gas) and deforestation. It is the most significant greenhouse gas contributing to human-induced global warming.
   • N$_{2}$ (Nitrogen): Makes up about 78% of the atmosphere and is chemically inert under normal conditions; it does not contribute to the greenhouse effect.
   • He (Helium): A noble gas that is chemically inert and does not trap heat in the atmosphere.

   3. Show the solution

   • Identify the gases: Oxygen, Carbon dioxide, Nitrogen, and Helium.
   • Evaluate their properties: Only Carbon dioxide (CO$_{2}$) has the molecular structure that allows it to absorb and re-emit infrared radiation, effectively trapping heat.
   • Conclusion: As human activities increase the concentration of CO$_{2}$ in the atmosphere, more heat is trapped, leading to a rise in global temperatures.

   4. Identify the answer

   The correct gas responsible for global warming among the options provided is Carbon dioxide.

   Correct Option: B

   5. Tip

   When you see questions about "Global Warming" or "Greenhouse Gases," always look for CO$_{2}$, Methane (CH$_{4}$), or Water Vapor. Remember that noble gases (like Helium) and diatomic gases (like N$_{2}$ and O$_{2}$) are generally not responsible for the greenhouse effect because they do not absorb infrared radiation effectively.

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3. 3.

   A sample of any of the following substances disappears after some time when exposed to air like camphor, naphthalene, or dry ice. This phenomenon is called?

   1. A.Sublimation
   2. B.Evaporation
   3. C.Diffusion
   4. D.Radiation

   Show answer

   Answer: A. Sublimation

   AI explanation

   Analysis

   The question asks for the name of the physical process where specific solid substances (camphor, naphthalene, and dry ice) transition directly into a gaseous state when exposed to air, without passing through the liquid phase.

   Concept Explanation

   In chemistry, matter typically exists in three states: solid, liquid, and gas. Usually, a solid must melt into a liquid before it can evaporate into a gas. However, some substances have unique properties where the intermolecular forces are weak enough that the solid can transition directly into a gas when heat is absorbed. This process is known as sublimation.

   • Sublimation: The direct change of state from solid to gas (e.g., camphor, naphthalene/mothballs, and dry ice/solid $CO_2$).
   • Evaporation: The process where a liquid turns into a gas at a temperature below its boiling point.
   • Diffusion: The movement of particles from an area of higher concentration to an area of lower concentration.
   • Radiation: The transfer of energy through electromagnetic waves.

   Step-by-Step Solution

   1. Identify the substances: Camphor, naphthalene, and dry ice are all solids at room temperature.
   2. Observe the behavior: When left in the open, these substances "disappear" or shrink in size without leaving any liquid residue behind.
   3. Apply the definition: Since they bypass the liquid state entirely, the process cannot be evaporation. Because they are changing state due to heat absorption from the environment, the process is defined as sublimation. 4.

   Exam Tip

   Whenever you see questions involving "mothballs" (naphthalene), "camphor," or "dry ice" disappearing, immediately think of sublimation. These are the classic examples used in JAMB and WASSCE chemistry exams to test your knowledge of changes of state.

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4. 4.

   The process or act of extracting a metal from its ore and refining it is called?

   1. A.Extraction
   2. B.Metal mining
   3. C.Mettallurgy
   4. D.Prospecting

   Show answer

   Answer: C. Mettallurgy

   AI explanation

   Analysis of the Question

   The question asks for the specific technical term used to describe the entire industrial process of obtaining a pure metal from its naturally occurring ore.

   Concept Explanation

   In Chemistry, the study and practice of metals involve several stages:

   1. Prospecting: This is the initial search for mineral deposits in the earth's crust.
   2. Mining: This is the physical act of digging or extracting the ore from the ground.
   3. Metallurgy: This is the broad branch of science and technology concerned with the properties of metals and their production. It specifically encompasses the processes of extracting metals from their ores (by reduction or electrolysis) and refining them to achieve the desired purity.

   Step-by-Step Solution

   • Step 1: Evaluate Option A (Extraction). While extraction is a part of the process, it is a general term and does not fully cover the "refining" aspect mentioned in the question.
   • Step 2: Evaluate Option B (Metal mining). This refers only to the physical removal of the ore from the earth, not the chemical processes required to isolate and purify the metal.
   • Step 3: Evaluate Option C (Metallurgy). By definition, metallurgy is the science and technology of extracting metals from their ores and modifying the metals for use (refining). This covers both the extraction and the purification/refining stages.
   • Step 4: Evaluate Option D (Prospecting). This is the preliminary stage of searching for the ore, not the processing stage.

   Conclusion

   The term that encompasses both the extraction of a metal from its ore and its subsequent refining is Metallurgy.

   Exam Tip: When you see questions about "extracting and refining," always look for the term "Metallurgy." If the question asks about the initial search for minerals, the answer is "Prospecting." If it asks about the physical removal from the ground, the answer is "Mining."

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5. 5.

   The reactions involving simultaneous oxidation and reduction?

   1. A.Automatic reactions
   2. B.Alternate reactions
   3. C.Reduction agency
   4. D.Redox reactions

   Show answer

   Answer: D. Redox reactions

   AI explanation

   Analysis

   The question asks for the specific term used to describe chemical reactions where both oxidation (loss of electrons) and reduction (gain of electrons) occur simultaneously.

   Concept Explanation

   In chemistry, oxidation and reduction are two halves of a single process.

   • Oxidation: The process where an atom or ion loses electrons (or gains oxygen/loses hydrogen).
   • Reduction: The process where an atom or ion gains electrons (or loses oxygen/gains hydrogen).

   Because electrons cannot simply disappear or appear out of nowhere, any substance that loses electrons (is oxidized) must transfer them to another substance that gains them (is reduced). Therefore, these two processes always happen together. We combine the terms Reduction and Oxidation to form the portmanteau Redox.

   Step-by-Step Solution

   1. Evaluate Option A (Automatic reactions): This is not a standard chemical term for these reactions.
   2. Evaluate Option B (Alternate reactions): While the processes alternate between atoms, this is not the scientific name for the reaction type.
   3. Evaluate Option C (Reduction agency): This refers to a "reducing agent," which is the substance that causes reduction by being oxidized itself. It is not the name of the reaction.
   4. Evaluate Option D (Redox reactions): As explained above, "Redox" is the standard scientific term derived from Reduction and Oxidation. It perfectly describes a reaction involving the simultaneous transfer of electrons.

   Conclusion

   Exam Tip: Remember the mnemonic OIL RIG:

   • Oxidation Is Loss (of electrons)
   • Reduction Is Gain (of electrons) If you see a reaction where one element's oxidation state increases and another's decreases, it is definitely a Redox reaction!

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6. 6.

   The most abundant rare gas in the atmosphere is?

   1. A.He
   2. B.Ne
   3. C.Ar
   4. D.Xe

   Show answer

   Answer: C. Ar

   AI explanation

   1. Analyze the question

   The question asks for the most abundant "rare gas" (also known as a noble gas or inert gas) found in the Earth's atmosphere.

   2. Explain the concept

   Noble gases are elements found in Group 18 of the periodic table. They are characterized by having a full valence shell, which makes them chemically inert (unreactive). While they are called "rare" gases, they exist in varying concentrations in the atmosphere.

   The composition of the Earth's atmosphere by volume is approximately:

   • Nitrogen ($N_2$): ~78%
   • Oxygen ($O_2$): ~21%
   • Argon ($Ar$): ~0.93%
   • Carbon dioxide ($CO_2$): ~0.04%
   • Trace amounts of other noble gases (Neon, Helium, Krypton, Xenon).

   3. Show the solution

   • Helium (He): Exists in the atmosphere in very small quantities (about 0.0005%).
   • Neon (Ne): Exists in even smaller quantities (about 0.0018%).
   • Argon (Ar): This is the third most abundant gas in the atmosphere after Nitrogen and Oxygen, with a concentration of approximately 0.93%.
   • Xenon (Xe): Exists in trace amounts (about 0.000009%).

   Comparing these values, Argon has the highest concentration among all the noble gases in the atmosphere.

   4. Identify the answer

   Based on the atmospheric composition data, Argon is significantly more abundant than Helium, Neon, or Xenon. Therefore, the correct option is C.

   5. Exam Tip

   To remember the order of abundance of noble gases in the atmosphere, use the mnemonic: "All Needy He-men Keep X-raying" (Argon > Neon > Helium > Krypton > Xenon). Always remember that Argon is the "odd one out" because it is the only noble gas present in a concentration close to 1%.

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7. 7.

   In troposphere, the two types of pollutants are?

   1. A.Gaseous and particulate pollutants
   2. B.Carbon and metallic pollutants
   3. C.Natural and man-made pollutants
   4. D.Sulphuric and nitrogenous pollutants

   Show answer

   Answer: A. Gaseous and particulate pollutants

   AI explanation

   Analysis

   The question asks for the classification of pollutants found in the troposphere (the lowest layer of the Earth's atmosphere). To answer this, we must look at the physical and chemical states of substances that contaminate the air.

   Concept Explanation

   Pollutants in the atmosphere are generally categorized based on their physical state:

   1. Gaseous Pollutants: These are substances that exist in the gaseous phase under normal atmospheric conditions. Common examples include oxides of carbon ($CO$, $CO_2$), oxides of nitrogen ($NO_x$), oxides of sulfur ($SO_x$), and hydrocarbons.
   2. Particulate Pollutants: These are minute solid particles or liquid droplets suspended in the air. Examples include dust, smoke, mist, fumes, and smog.

   Step-by-Step Solution

   • Step 1: Evaluate the options provided.
   • Step 2: Option B and D are too specific (they only name certain types of chemicals, not the broad categories).
   • Step 3: Option C refers to the source of the pollutants (where they come from), not the type of pollutant itself.
   • Step 4: Option A correctly identifies the two primary physical forms in which pollutants exist in the troposphere: gases and particulate matter. This is the standard scientific classification used in environmental chemistry.

   Conclusion

   The troposphere is contaminated by both gases (like $SO_2$ and $NO_2$) and particulate matter (like smoke and soot). Therefore, the most accurate classification is gaseous and particulate pollutants.

   Exam Tip: When you see questions about atmospheric pollution, always remember the "Gaseous vs. Particulate" divide. If you are asked about the source, then look for "Natural vs. Anthropogenic (man-made)." Don't let the terminology confuse you!

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8. 8.

   The inherited traits of an organism are controlled by?

   1. A.RNA molecules
   2. B.Nucleotides
   3. C.DNA molecules
   4. D.Enzymes

   Show answer

   Answer: C. DNA molecules

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9. 9.

   Oxygen is absent in?

   1. A.Kerosene
   2. B.Soil
   3. C.Glass
   4. D.Cement

   Show answer

   Answer: A. Kerosene

   AI explanation

   Analysis

   The question asks us to identify which of the listed substances does not contain oxygen in its chemical composition. We need to look at the chemical makeup of each option.

   Concept Explanation

   • Soil: Soil is a complex mixture containing minerals, organic matter, water, and air. Minerals in soil (like silicates and oxides) and water ($H_2O$) contain oxygen.
   • Glass: Common glass (soda-lime glass) is primarily made of silica ($SiO_2$), along with sodium oxide ($Na_2O$) and calcium oxide ($CaO$). Oxygen is a major component here.
   • Cement: Cement is typically made from limestone ($CaCO_3$), clay, and other minerals. These compounds are rich in oxygen (e.g., $CaO$, $SiO_2$, $Al_2O_3$).
   • Kerosene: Kerosene is a mixture of hydrocarbons obtained from the fractional distillation of petroleum. Hydrocarbons consist exclusively of carbon and hydrogen atoms ($C_nH_{2n+2}$).

   Step-by-Step Solution

   1. Evaluate Soil: Soil contains water ($H_2O$) and various mineral oxides. Oxygen is present.
   2. Evaluate Glass: Glass is composed of silica ($SiO_2$) and other metal oxides. Oxygen is present.
   3. Evaluate Cement: Cement is composed of complex calcium silicates and aluminates, all of which contain oxygen. Oxygen is present.
   4. Evaluate Kerosene: Kerosene is a hydrocarbon fuel. By definition, hydrocarbons are organic compounds consisting entirely of hydrogen and carbon. There are no oxygen atoms in the molecular structure of pure kerosene.

   Conclusion

   Since kerosene is a hydrocarbon, it is the only substance among the options that lacks oxygen in its chemical structure.

   Exam Tip: Whenever you see questions about the composition of fuels like petrol, diesel, or kerosene, remember they are hydrocarbons ($C_xH_y$). They are distinct from substances like carbohydrates or alcohols, which do contain oxygen.

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10. 10.

    The fourteen elements (atomic number 90-103) after actinium are called?

    1. A.Actinoids
    2. B.Nucleotides
    3. C.Pre-actinum elements
    4. D.Atomic elements

    Show answer

    Answer: A. Actinoids

    AI explanation

    1. Analyze the question

    The question asks for the specific name given to the series of 14 chemical elements that follow Actinium (atomic number 89) in the periodic table, specifically those with atomic numbers 90 through 103.

    2. Explain the concept

    In the periodic table, there are two rows of elements usually placed at the bottom to prevent the table from becoming too wide.

    • The first row (atomic numbers 57–71) follows Lanthanum and is called the Lanthanoids (or Lanthanides).
    • The second row (atomic numbers 89–103) follows Actinium. These elements are known as the Actinoids (or Actinides).

    These elements are characterized by the filling of the 5f electron subshell. Because they all share similar chemical properties to Actinium, they are grouped together in this series.

    3. Show the solution

    • Step 1: Identify the position of Actinium in the periodic table. Actinium has an atomic number of 89.
    • Step 2: Identify the elements that follow it. The elements from atomic number 90 (Thorium) to 103 (Lawrencium) are placed in the f-block of the periodic table.
    • Step 3: Apply the nomenclature rule. Just as elements following Lanthanum are called Lanthanoids, elements following Actinium are named Actinoids.
    • Step 4: Evaluate the options. • A. Actinoids: This matches the standard chemical nomenclature for this series. • B. Nucleotides: These are biological molecules (the building blocks of DNA/RNA), not chemical elements. • C. Pre-actinum elements: This is incorrect as these elements come after Actinium, not before. • D. Atomic elements: This is a generic term that applies to all elements, not a specific group name.

    4. Identify the answer

    The correct term for the series of elements from atomic number 90 to 103 is Actinoids.

    5. Exam Tip

    To remember this easily, think of the "f-block" elements as the "bottom-block" elements. Remember: Lanthanoids start with Lanthanum (Atomic number 57), and Actinoids start with Actinium (Atomic number 89).

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11. 11.

    The nucleus of a hydrogen  atom consist of a?

    1. A.1 proton only
    2. B.1 proton, 2 neutron
    3. C.1 neutron only
    4. D.1 electron only

    Show answer

    Answer: A. 1 proton only

    AI explanation

    Analysis

    The question asks for the subatomic composition of the nucleus of a standard hydrogen atom. To answer this, we must look at the atomic structure of the most common isotope of hydrogen, known as Protium ($^1_1H$).

    Concept

    • Atomic Structure: An atom consists of a central nucleus containing protons and neutrons, surrounded by electrons in shells.
    • Hydrogen Atom: Hydrogen is the simplest element in the periodic table. Its atomic number is 1, which means it has 1 proton. Its mass number is also 1.
    • The Nucleus: The mass number is the sum of protons and neutrons. Since the mass number is 1 and the number of protons is 1, the number of neutrons must be $1 - 1 = 0$.
    • Electrons: Electrons are found outside the nucleus, not inside it.

    Step-by-Step Solution

    1. Identify the Atomic Number ($Z$): For hydrogen, $Z = 1$. This confirms there is 1 proton.
    2. Identify the Mass Number ($A$): For the most common hydrogen atom, $A = 1$.
    3. Calculate Neutrons ($N$): Using the formula $N = A - Z$, we get $N = 1 - 1 = 0$. Therefore, there are no neutrons in the nucleus of a standard hydrogen atom.
    4. Evaluate the Options: • A: 1 proton only — This is correct because there are no neutrons and the electron is outside the nucleus. • B: 1 proton, 2 neutrons — This describes Tritium, a radioactive isotope of hydrogen, not the standard hydrogen atom. • C: 1 neutron only — Incorrect; hydrogen has no neutrons in its nucleus. • D: 1 electron only — Incorrect; electrons are located in the orbital shells, not the nucleus.

    Conclusion

    The nucleus of a standard hydrogen atom consists solely of a single proton.

    Exam Tip

    Remember the acronym PEN: Protons and Electrons are equal in a neutral atom, but Neutrons are calculated by subtracting the atomic number from the mass number. For hydrogen, the "N" is zero, making it the only element in the periodic table without a neutron in its nucleus!

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12. 12.

    Which of the following are chemical changes?  I. cooking of food II. digestion of food III. freezing of water IV. water is heated up

    1. A.I and II
    2. B.I, II, and III
    3. C.III and IV
    4. D.all of the above

    Show answer

    Answer: A. I and II

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13. 13.

    The enzyme that converts glucose to ethyl alcohol is?

    1. A.maltase
    2. B.zymase
    3. C.Diatase
    4. D.Invertase

    Show answer

    Answer: B. zymase

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14. 14.

    The scientist who stated that matter can be converted into energy is?

    1. A.Boyle
    2. B.Lavoiser
    3. C.Avogadro
    4. D.Einstein

    Show answer

    Answer: D. Einstein

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15. 15.

    The nucleus of an atom consists of?

    1. A.Electrons and neutrons
    2. B.Electrons and protons
    3. C.Protons and neutrons
    4. D.None of the above

    Show answer

    Answer: C. Protons and neutrons

    AI explanation

    1. Analyze the question

    The question asks for the subatomic particles that make up the central core (nucleus) of an atom.

    2. Explain the concept

    An atom is composed of three main subatomic particles:

    • Protons: Positively charged particles found inside the nucleus.
    • Neutrons: Neutral particles (no charge) also found inside the nucleus.
    • Electrons: Negatively charged particles that orbit the nucleus in specific energy levels or shells.

    The nucleus is the dense, central part of the atom where almost all of its mass is concentrated. Because protons and neutrons are located here, they are collectively referred to as nucleons.

    3. Show the solution

    • Step 1: Identify the location of electrons. Electrons are located in the shells (or orbitals) surrounding the nucleus, not inside it. This eliminates options A and B.
    • Step 2: Identify the location of protons and neutrons. Protons and neutrons are tightly packed together at the center of the atom, forming the nucleus.
    • Step 3: Compare with the given options. Since the nucleus contains only protons and neutrons, option C is the correct description.

    4. Identify the answer

    The correct option is C.

    5. Exam Tip

    To remember this easily, use the mnemonic "P-N" for Protons and Neutrons in the Nucleus. Think of the nucleus as the "heavy" part of the atom; since electrons have negligible mass compared to protons and neutrons, they stay outside the nucleus, while the "heavy" particles stay inside.

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16. 16.

    The compounds made up of only carbon and hydrogen are called?

    1. A.Carbon compounds
    2. B.Hydrocarbons
    3. C.Atoms
    4. D.Carbon hydrolysis

    Show answer

    Answer: B. Hydrocarbons

    AI explanation

    Analysis

    The question asks for the specific classification of chemical compounds that consist exclusively of two elements: carbon and hydrogen.

    Concept Explanation

    In organic chemistry, compounds are classified based on their elemental composition.

    • Hydrocarbons are the simplest organic compounds. As the name suggests ("hydro" for hydrogen and "carbon" for carbon), they are molecules that contain only carbon and hydrogen atoms bonded together.
    • They form the foundation of organic chemistry and are categorized into groups like alkanes, alkenes, alkynes, and aromatics (like benzene).
    • Other options like "Carbon compounds" is a broad term that includes things like carbon dioxide ($CO_2$) or carbonates, which contain oxygen and are not hydrocarbons.

    Step-by-Step Solution

    1. Identify the components: The question specifies "only carbon and hydrogen."
    2. Evaluate Option A: "Carbon compounds" is too general. It includes substances like $CaCO_3$ (calcium carbonate), which contains oxygen.
    3. Evaluate Option B: "Hydrocarbons" are defined by IUPAC as compounds consisting entirely of hydrogen and carbon. This matches the criteria perfectly.
    4. Evaluate Option C: "Atoms" are the basic building blocks of matter, not compounds.
    5. Evaluate Option D: "Carbon hydrolysis" is a chemical reaction involving water, not a classification of a compound.

    Conclusion

    Since the definition of a hydrocarbon is a compound containing only carbon and hydrogen, Option B is the correct classification.

    Exam Tip

    Whenever you see the prefix "Hydro-" in chemistry, think of hydrogen. When you see "-carbon," think of carbon. Combining them gives you the exact definition! This is a common "free mark" question in JAMB, so ensure you remember that hydrocarbons are the parent class of all organic molecules.

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17. 17.

    The mass of one Avogadro number of helium atoms is?

    1. A.1.00gram
    2. B.4.00gram
    3. C.8.00gram
    4. D.6.00gram

    Show answer

    Answer: B. 4.00gram

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18. 18.

    Which one of the following is not a mixture?

    1. A.Air
    2. B.Mercury
    3. C.Milk
    4. D.Cement

    Show answer

    Answer: B. Mercury

    AI explanation

    Analysis

    The question asks us to identify which of the given substances is not a mixture. In chemistry, a mixture consists of two or more substances that are physically combined but not chemically bonded. A substance that is not a mixture must be either an element or a compound (a pure substance).

    Concept Explanation

    • Mixture: A material made up of two or more different substances which are mixed but are not combined chemically. They can be separated by physical means (e.g., filtration, distillation, or evaporation).
    • Pure Substance: A substance that has a constant composition and distinct chemical properties. It cannot be separated into simpler substances by physical means. Pure substances are either elements (like Mercury) or compounds (like Water or Sodium Chloride).

    Step-by-Step Solution

    1. Analyze Option A (Air): Air is a mixture of various gases, including nitrogen, oxygen, argon, carbon dioxide, and water vapor. Since it contains multiple substances physically mixed together, it is a mixture.
    2. Analyze Option B (Mercury): Mercury is a chemical element with the symbol Hg and atomic number 80. It consists of only one type of atom. Because it is a pure element, it is not a mixture.
    3. Analyze Option C (Milk): Milk is a complex mixture (specifically a colloid) containing water, fats, proteins (casein), lactose, and minerals. It is not a pure substance.
    4. Analyze Option D (Cement): Cement is a mixture of various compounds, including calcium silicates, aluminates, and other additives. It is a heterogeneous mixture.

    Conclusion

    Since Mercury is a pure element, it does not fit the definition of a mixture.

    Exam Tip

    When you see a question asking for "what is not a mixture," look for the pure substance. If you see a metal (like Iron, Copper, or Mercury) or a simple chemical formula (like $H_2O$ or $NaCl$), that is almost certainly your answer!

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19. 19.

    Neutrons were discovered by?

    1. A.James Chadwick
    2. B.Ernest Rutherford
    3. C.J.J Thompson
    4. D.John Dalton

    Show answer

    Answer: A. James Chadwick

    AI explanation

    Analysis

    The question asks for the scientist credited with the discovery of the neutron, a subatomic particle found in the nucleus of an atom.

    Concept

    To answer this, we must look at the history of atomic theory and the key scientists involved in discovering the components of the atom:

    • John Dalton: Proposed the atomic theory, suggesting atoms are indivisible spheres.
    • J.J. Thomson: Discovered the electron using cathode ray tubes (the "Plum Pudding" model).
    • Ernest Rutherford: Discovered the nucleus and the proton through his famous gold foil experiment.
    • James Chadwick: Conducted experiments in 1932 bombarding beryllium with alpha particles, which led to the discovery of a neutral particle with a mass similar to the proton—the neutron.

    Solution

    1. Evaluate the options: • John Dalton (D): Known for his early atomic theory, not the discovery of subatomic particles. • J.J. Thomson (C): Discovered the electron. • Ernest Rutherford (B): Discovered the proton and the atomic nucleus. • James Chadwick (A): Successfully identified the neutron, completing our basic understanding of the atom's structure.
    2. Conclusion: James Chadwick is the scientist who experimentally confirmed the existence of the neutron in 1932.

    Exam Tip

    A great way to remember this for your JAMB exam is the mnemonic "PEN":

    • Proton: Rutherford
    • Electron: Thomson
    • Neutron: Chadwick (Think: Proton-Rutherford, Electron-Thomson, Neutron-Chadwick).

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20. 20.

    The process by which salt and water reacted in a limited way to form an acid or a base is?

    1. A.Neutral process
    2. B.Basic acidic process
    3. C.Hydrolysis
    4. D.Sublimation

    Show answer

    Answer: C. Hydrolysis

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21. 21.

    The molar enthalpy change accompanying the removal of an electron from a gas phase atom or ion in its ground state is called?

    1. A.Electron gain enthalpy
    2. B.Ionization enthalpy
    3. C.Enthalpy change
    4. D.Enthalpic gas removal

    Show answer

    Answer: B. Ionization enthalpy

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22. 22.

    An element having the atomic number 17 will resemble which of the following elements having atomic number as given below?

    1. A.33
    2. B.35
    3. C.18
    4. D.19

    Show answer

    Answer: B. 35

    AI explanation

    1. Analyze the Question

    The question asks us to identify which element (given by its atomic number) shares similar chemical properties with an element that has an atomic number of 17.

    2. Explain the Concept

    In chemistry, elements in the same group (vertical column) of the Periodic Table exhibit similar chemical properties because they have the same number of valence electrons (electrons in their outermost shell).

    • Step 1: Determine the electronic configuration of the element with atomic number 17.
    • Step 2: Identify its group.
    • Step 3: Determine the electronic configuration of the options provided to see which one falls into the same group.

    3. Show the Solution

    Step 1: Electronic configuration of atomic number 17 (Chlorine)

    • Configuration: $1s^2 2s^2 2p^6 3s^2 3p^5$
    • Valence electrons: $2 + 5 = 7$
    • This element is in Group 7 (the Halogens). Elements in this group have 7 valence electrons and tend to gain one electron to achieve a stable octet.

    Step 2: Check the options for the same valence electron count

    • Option A (33): $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^3$. Valence electrons = 5. (Group 5)
    • Option B (35): $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^5$. Valence electrons = 7. (Group 7)
    • Option C (18): $1s^2 2s^2 2p^6 3s^2 3p^6$. Valence electrons = 8. (Group 0/8 - Noble Gas)
    • Option D (19): $1s^2 2s^2 2p^6 3s^2 3p^6 4s^1$. Valence electrons = 1. (Group 1 - Alkali Metal)

    Step 3: Compare Since atomic number 35 also has 7 valence electrons in its outermost shell ($4s^2 4p^5$), it belongs to the same group as atomic number 17. Therefore, they will exhibit similar chemical properties.

    4. Identify the Answer

    The element with atomic number 35 (Bromine) is in the same group as the element with atomic number 17 (Chlorine). Both are halogens.

    5. Exam Tip

    To quickly find the group of an element, look at the last number in its shell configuration (e.g., 2, 8, 7). If the last number is 1, 2, or 3, it's a metal. If it's 5, 6, or 7, it's a non-metal. Elements in the same group always have the same number of valence electrons!

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23. 23.

    The atomic weight of nitrogen is?

    1. A.10
    2. B.12
    3. C.14
    4. D.16

    Show answer

    Answer: C. 14

    AI explanation

    Analysis

    The question asks for the standard atomic weight (or relative atomic mass) of the element Nitrogen. In chemistry, this value represents the average mass of an atom of an element compared to one-twelfth of the mass of a carbon-12 atom.

    Concept

    The periodic table organizes elements based on their atomic number (number of protons). Nitrogen is the 7th element in the periodic table. Its most abundant isotope is Nitrogen-14, which consists of 7 protons and 7 neutrons. While there are trace amounts of other isotopes (like Nitrogen-15), the weighted average mass used in standard chemical calculations is approximately 14.007, which is rounded to 14 for most secondary school examinations.

    Solution

    1. Identify the element: Nitrogen (Symbol: N).
    2. Locate in the Periodic Table: Nitrogen is in Group 5, Period 2, with an atomic number of 7.
    3. Determine the mass number: The mass number is the sum of protons and neutrons. For the most common isotope of Nitrogen, $7 \text{ protons} + 7 \text{ neutrons} = 14$.
    4. Compare with options: • A: 10 (Incorrect) • B: 12 (This is the atomic weight of Carbon) • C: 14 (Correct) • D: 16 (This is the atomic weight of Oxygen)

    Exam Tip

    To remember atomic weights for common elements, use the "Even Atomic Number Rule" for light elements: for many elements with an even atomic number (like Carbon-6, Oxygen-8, Neon-10), the atomic weight is roughly double the atomic number. Nitrogen is an exception to this rule because it has an odd atomic number (7), but its mass is 14. Just remember: Nitrogen is 7, so double it to get 14!

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24. 24.

    The reactivity of fluorine is due to?

    1. A.its high electro negativity
    2. B.small size of fluorine atom
    3. C.availability of D-orbitals
    4. D.strong f-f bond

    Show answer

    Answer: A. its high electro negativity

    AI explanation

    Analysis

    The question asks for the primary reason behind the extreme reactivity of fluorine compared to other halogens in Group 7 of the periodic table.

    Concept Explanation

    Fluorine is the most electronegative and the most reactive non-metal in the periodic table. To understand its reactivity, we look at two main factors:

    1. Electronegativity: This is the tendency of an atom to attract a shared pair of electrons in a covalent bond. Fluorine has the highest electronegativity of all elements (4.0 on the Pauling scale). Because it pulls electrons so strongly, it reacts vigorously with almost any substance it encounters.
    2. Bond Dissociation Energy: While fluorine is small, the F-F bond is actually surprisingly weak compared to other halogens (like Cl-Cl) due to the repulsion between the lone pairs of electrons on the small fluorine atoms. This makes it very easy to break the bond and initiate a reaction.

    However, in the context of standard chemistry examinations like JAMB, the high electronegativity is the fundamental property that drives its ability to gain an electron and form bonds, making it the most reactive element in the group.

    Step-by-Step Solution

    1. Examine Option A: Electronegativity is the measure of an atom's ability to attract electrons. Since fluorine has the highest electronegativity, it has the strongest drive to complete its valence shell, making it highly reactive.
    2. Examine Option B: While the small size contributes to the high electronegativity, "high electronegativity" is the more direct chemical explanation for its reactivity.
    3. Examine Option C: Fluorine is in the second period and does not have d-orbitals. This is factually incorrect.
    4. Examine Option D: The F-F bond is weak, but the reactivity of the element itself is defined by its electronic nature (electronegativity) rather than just the bond strength of the diatomic molecule.

    Comparing these, the most comprehensive reason for fluorine's chemical behavior is its extreme electronegativity.

    Conclusion

    This aligns with the chemical principle that fluorine's position as the most electronegative element is the primary driver of its chemical reactivity.

    Exam Tip

    Remember the acronym FONCl (Fluorine, Oxygen, Nitrogen, Chlorine). These are the most electronegative elements in order. Fluorine is the "king" of electronegativity—whenever you see a question about why fluorine is so reactive or why it forms such strong ionic bonds, look for "electronegativity" as your keyword!

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25. 25.

    A chemical process in which there is a gain of electrons is known as?

    1. A.Sublimation
    2. B.Reduction
    3. C.Oxidation
    4. D.Distillation

    Show answer

    Answer: B. Reduction

    AI explanation

    Analysis

    The question asks for the definition of a chemical process characterized by the gain of electrons. This is a fundamental concept in electrochemistry and redox (reduction-oxidation) reactions.

    Concept Explanation

    To understand this, we use the popular mnemonic OIL RIG:

    • Oxidation Is Loss (of electrons)
    • Reduction Is Gain (of electrons)

    In any redox reaction, electrons are transferred from one species to another. The species that gains electrons undergoes a decrease in its oxidation state, which is defined as reduction. Conversely, the species that loses electrons undergoes an increase in its oxidation state, which is defined as oxidation.

    Step-by-Step Solution

    1. Evaluate Option A (Sublimation): This is a physical process where a solid changes directly into a gas without passing through the liquid phase. It does not involve electron transfer.
    2. Evaluate Option B (Reduction): By definition, reduction is the gain of electrons. For example, in the reaction $Cl_2 + 2e^- \rightarrow 2Cl^-$, chlorine gains electrons and is reduced.
    3. Evaluate Option C (Oxidation): By definition, oxidation is the loss of electrons. For example, in the reaction $Na \rightarrow Na^+ + e^-$, sodium loses an electron and is oxidized.
    4. Evaluate Option D (Distillation): This is a physical process used to separate mixtures based on differences in boiling points. It does not involve electron transfer.

    Since the question specifically asks for the process involving the gain of electrons, the correct term is reduction.

    Exam Tip

    Whenever you see a question about electron transfer, immediately write "OIL RIG" on your scratch paper. It is a foolproof way to ensure you don't mix up oxidation and reduction during the pressure of the exam.

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26. 26.

    Which of the following is a form of calcium carbonate? I. limestone II. marble III. chalk Iv. egg-shells

    1. A.I only
    2. B.I, II and IV
    3. C.I and II only
    4. D.I, II, III, and IV

    Show answer

    Answer: D. I, II, III, and IV

    AI explanation

    Analysis

    The question asks us to identify which of the listed substances are forms of calcium carbonate ($CaCO_3$). We need to evaluate each item to see if it is chemically composed primarily of calcium carbonate.

    Concept Explanation

    Calcium carbonate is a naturally occurring chemical compound. It is the main component of many geological formations and biological structures.

    • Limestone: A sedimentary rock composed mainly of skeletal fragments of marine organisms such as coral and mollusks. It is essentially calcium carbonate.
    • Marble: A metamorphic rock formed when limestone is subjected to high heat and pressure. It is a recrystallized form of calcium carbonate.
    • Chalk: A soft, white, porous sedimentary carbonate rock, a form of limestone composed of the mineral calcite ($CaCO_3$).
    • Egg-shells: The hard outer covering of the eggs of birds and some reptiles. It is composed primarily of calcium carbonate crystals stabilized by a protein matrix.

    Step-by-Step Solution

    1. Evaluate I (Limestone): Limestone is widely known as a sedimentary rock consisting of $CaCO_3$. (Correct)
    2. Evaluate II (Marble): Marble is metamorphosed limestone, meaning it retains the chemical composition of $CaCO_3$. (Correct)
    3. Evaluate III (Chalk): Chalk is a specific, soft variety of limestone, which is $CaCO_3$. (Correct)
    4. Evaluate IV (Egg-shells): Biological studies confirm that the primary mineral component of an eggshell is calcium carbonate. (Correct)

    Since all four items (I, II, III, and IV) are forms or sources of calcium carbonate, they all satisfy the condition of the question.

    Conclusion

    Comparing our findings with the provided options, we see that all four items are included in option D.

    Exam Tip: When you see a question listing multiple items like this, remember that calcium carbonate is very common in nature. If you recognize that most of the items are definitely $CaCO_3$, look for an option that includes all of them rather than trying to eliminate one unless you are certain it is chemically different.

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27. 27.

    The heat required to raise the temperature of the body by 1k is called?

    1. A.Specific heat
    2. B.Thermal capacity
    3. C.Water equivalent
    4. D.None of the above

    Show answer

    Answer: B. Thermal capacity

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28. 28.

    Give the common name for the following compound (CH$_{3}$)$_{2}$ CH CH$_{2}$ -Br

    1. A.Isobutyl bromide
    2. B.Methyl bromide
    3. C.propyl bromide
    4. D.Butyl bromide

    Show answer

    Answer: A. Isobutyl bromide

    AI explanation

    Analysis of the Question

    The compound given is $(CH_{3})_{2}CHCH_{2}-Br$. We need to identify its common (trivial) name based on the arrangement of the carbon chain and the position of the functional group (Bromine).

    Concept Explanation

    In organic chemistry, common naming conventions use prefixes like n- (normal), iso-, and neo- to describe the structure of alkyl groups:

    • n- (normal): A straight chain of carbons.
    • iso-: A structure where there is a methyl group ($-CH_{3}$) attached to the second-to-last carbon atom of the chain.
    • Butyl group: Contains 4 carbon atoms.

    Looking at the structure $(CH_{3})_{2}CHCH_{2}-Br$:

    1. Count the total number of carbons: There are 3 carbons in the $(CH_{3})_{2}CH$ part and 1 carbon in the $CH_{2}$ part, totaling 4 carbons. This makes it a butyl derivative.
    2. Examine the branching: The structure has a $(CH_{3})_{2}CH-$ group at the end of the chain. This specific branching pattern (a "V" shape at the end of the chain) is the hallmark of an isobutyl group.

    Step-by-Step Solution

    1. Expand the structure: $CH_{3} - CH(CH_{3}) - CH_{2} - Br$
    2. Identify the alkyl group: The carbon attached to the Bromine ($CH_{2}$) is connected to a $CH$ group, which is further branched with two methyl groups. This configuration is defined as isobutyl.
    3. Attach the functional group: Since the functional group is Bromine ($-Br$), the compound is named isobutyl bromide.

    Comparison with Options

    • A. Isobutyl bromide: Matches our structural analysis.
    • B. Methyl bromide: Incorrect; this would be $CH_{3}Br$.
    • C. Propyl bromide: Incorrect; this would have only 3 carbons.
    • D. Butyl bromide: This usually refers to n-butyl bromide ($CH_{3}CH_{2}CH_{2}CH_{2}Br$), which is a straight chain.

    Exam Tip

    When naming alkyl halides, always count the total number of carbons first to determine the root (methyl, ethyl, propyl, butyl). Then, look at the branching: if you see a $(CH_{3})_{2}CH-$ group at the end, it is almost certainly an "iso" compound!

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29. 29.

    A binary compound of oxygen with another element is referred to as?

    1. A.Oxide
    2. B.Element
    3. C.Carbon
    4. D.Nitrogen

    Show answer

    Answer: A. Oxide

    AI explanation

    1. Analyze the question

    The question asks for the specific chemical term used to describe a compound formed when oxygen combines with only one other element.

    2. Explain the concept

    In chemistry, nomenclature (the naming of compounds) often follows specific rules based on the elements involved:

    • Binary Compound: This is a chemical compound containing exactly two different elements.
    • Oxygen's Role: When oxygen is one of the two elements in a binary compound, the resulting substance is classified as an oxide.
    • Examples: • $MgO$ (Magnesium + Oxygen) = Magnesium oxide • $CO_2$ (Carbon + Oxygen) = Carbon dioxide • $H_2O$ (Hydrogen + Oxygen) = Hydrogen oxide (commonly known as water)

    3. Show the solution

    • Option A (Oxide): By definition, an oxide is a binary compound of oxygen with another element. This fits the description perfectly.
    • Option B (Element): An element is a pure substance consisting of only one type of atom. Since the question specifies a "compound," this is incorrect.
    • Option C (Carbon): Carbon is an element, not a class of compounds. While carbon can form an oxide (like $CO_2$), it is not the general term for all such compounds.
    • Option D (Nitrogen): Similar to carbon, nitrogen is an element. It can form oxides (like $NO_2$), but it is not the name for the category of compounds.

    4. Identify the answer

    The correct term for a binary compound of oxygen with another element is an Oxide. This matches option A.

    5. Exam Tip

    Whenever you see the suffix "-ide" in inorganic chemistry, it usually indicates a binary compound (e.g., Chloride, Sulfide, Nitride). If you see the prefix "Ox-", it is a strong indicator that the compound contains oxygen.

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30. 30.

    What is the chemical name for the compound CuCO$_{3}$?

    1. A.Copper (iii) carbonate
    2. B.Copper (ii) carbonate
    3. C.Copper (i) carbonate
    4. D.Copper

    Show answer

    Answer: B. Copper (ii) carbonate

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31. 31.

    Which of the following is a non-metal that remains liquid at room temperature?

    1. A.Chlorine
    2. B.Phosphorus
    3. C.Bromine
    4. D.Helium

    Show answer

    Answer: C. Bromine

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32. 32.

    A 'breath test' used by traffic police to check drunken driving uses?

    1. A.Tumeric on filter paper
    2. B.Silica gel coated with saliva nitrate
    3. C.Potassium permanganate-sulphuric acid
    4. D.Potassium dichromatic-sulphuric acid

    Show answer

    Answer: D. Potassium dichromatic-sulphuric acid

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33. 33.

    The only metal that is anti-bacterial is?

    1. A.Iron
    2. B.Sodium
    3. C.Alluminium
    4. D.Copper

    Show answer

    Answer: D. Copper

    AI explanation

    Analysis

    The question asks for the specific metal among the given options that possesses anti-bacterial (or oligodynamic) properties. This means the metal has the ability to kill or inhibit the growth of microorganisms like bacteria, viruses, and fungi.

    Concept Explanation

    The phenomenon where metal ions (especially heavy metals) exhibit a toxic effect on living cells, including bacteria, is known as the oligodynamic effect.

    While several metals (like silver and gold) are well-known for this, among the options provided, Copper is scientifically recognized for its potent antimicrobial properties. When bacteria come into contact with a copper surface, the copper ions disrupt the bacterial cell membrane, create oxidative stress, and damage the DNA of the bacteria, effectively killing them. This is why copper is frequently used in hospitals for surfaces like door handles and bed rails to reduce the spread of infections.

    Step-by-Step Solution

    1. Evaluate Iron (A): Iron is essential for biological processes (like oxygen transport in hemoglobin) but does not possess significant intrinsic anti-bacterial properties.
    2. Evaluate Sodium (B): Sodium is a highly reactive alkali metal. It reacts violently with water and is not used for its anti-bacterial properties.
    3. Evaluate Aluminium (C): Aluminium is widely used for its lightweight and corrosion-resistant properties, but it is not classified as an anti-bacterial metal.
    4. Evaluate Copper (D): Copper is widely documented in chemistry and microbiology for its oligodynamic effect, making it the correct choice for an anti-bacterial metal.

    Conclusion

    Based on the chemical properties of the metals listed, Copper is the only one that acts as an effective anti-bacterial agent.

    Exam Tip

    When you see questions about "anti-bacterial" or "antimicrobial" metals in your Chemistry or Biology exams, always look for Copper (Cu) or Silver (Ag). These are the two most common answers in Nigerian secondary school examinations regarding this specific property.

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34. 34.

    A solution contains 20g of solute in 180g of solvent. If the solvent is water, what is the concentration of the solution in terms of mass by mass percentage

    1. A.11.%
    2. B.22.2%
    3. C.10%
    4. D.20%

    Show answer

    Answer: C. 10%

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35. 35.

    What is the IUPAC name for the following compound? HC$\equiv$CCH$_{3}$

    1. A.Acetylene
    2. B.Methyl acetylene
    3. C.Butanol
    4. D.Decanoic acid

    Show answer

    Answer: B. Methyl acetylene

    AI explanation

    Analysis

    The question asks for the IUPAC name of the hydrocarbon with the structural formula HC$\equiv$CCH$_{3}$.

    Concept

    To name this compound, we look at the functional group present:

    1. Functional Group: The triple bond ($\equiv$) indicates that this compound belongs to the alkyne family.
    2. Carbon Chain Length: There are 3 carbon atoms in the chain. The prefix for 3 carbons is "prop-".
    3. IUPAC Naming Rule: For alkynes, the suffix is "-yne". Therefore, the systematic IUPAC name is propyne.

    Solution

    Let's evaluate the options provided:

    • A. Acetylene: This is the common name for ethyne ($HC\equiv CH$), not the compound in the question.
    • B. Methyl acetylene: This is the common name for propyne. While it is not the systematic IUPAC name (which is propyne), in many JAMB past questions, this is often the intended answer when "propyne" is not listed as an option.
    • C. Butanol: This is an alcohol (contains an -OH group), which is incorrect.
    • D. Decanoic acid: This is a carboxylic acid, which is incorrect.

    In the context of older or specific JAMB question banks, common names are sometimes accepted as the IUPAC name for simple hydrocarbons.

    Tip

    When naming hydrocarbons, always count the longest carbon chain first. If you see a triple bond, look for the "-yne" suffix. If the systematic name isn't there, look for the common name that describes the structure (like "methyl" attached to "acetylene").

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36. 36.

    One of the following is not a physical property of monosaccharides?

    1. A.Monosaccharides get charred when heated
    2. B.Monosaccharides are water-soluble, sweet substances
    3. C.They are highly vital to the exploration of metals
    4. D.They can be reduced to sugar alcohols

    Show answer

    Answer: C. They are highly vital to the exploration of metals

    AI explanation

    Analysis

    The question asks us to identify which of the given options is not a physical property of monosaccharides. Monosaccharides (like glucose and fructose) are the simplest form of carbohydrates.

    Concept Explanation

    • Physical Properties: These are characteristics that can be observed or measured without changing the chemical identity of the substance. Common physical properties of monosaccharides include their solubility in water, their sweet taste, and their crystalline nature.
    • Chemical Properties: These describe how a substance behaves during a chemical reaction (e.g., reacting with other substances, decomposition, or reduction).

    Step-by-Step Evaluation

    • Option A (Charring): When heated, monosaccharides undergo dehydration and decomposition, leaving behind carbon (charring). This is a chemical change/property.
    • Option B (Solubility and Taste): Monosaccharides are polar molecules due to their hydroxyl (-OH) groups, making them highly soluble in water. They are also known for their sweet taste. These are classic physical properties.
    • Option C (Exploration of metals): The exploration of metals (mining and metallurgy) involves geology, chemistry, and engineering. Monosaccharides have no role or relevance in the exploration or extraction of metals. This statement is factually incorrect in the context of chemistry.
    • Option D (Reduction): The reduction of monosaccharides to sugar alcohols (like sorbitol) is a chemical reaction involving the conversion of the carbonyl group to a hydroxyl group.

    Conclusion

    While options A and D describe chemical properties rather than physical ones, Option C is the most distinct outlier because it is completely unrelated to the nature or behavior of monosaccharides. In the context of this JAMB question, the examiners are looking for the statement that is entirely false regarding the nature of these sugars.

    Exam Tip

    When you see a "Which of the following is NOT..." question, always look for the option that sounds completely out of place or scientifically irrelevant to the topic. Often, the "odd one out" is the correct answer.

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37. 37.

    The mass number of a nucleus is?

    1. A.Always less than its atomic number
    2. B.The sum of the number of protons and neutrons present in the nucleus
    3. C.Always more than the atomic weight
    4. D.A fraction

    Show answer

    Answer: B. The sum of the number of protons and neutrons present in the nucleus

    AI explanation

    Analysis

    The question asks for the definition of the "mass number" of an atom. To answer this, we need to recall the fundamental structure of an atom and how its subatomic particles contribute to its total mass.

    Concept Explanation

    An atom consists of a central nucleus containing protons and neutrons, surrounded by electrons orbiting in shells.

    • Atomic Number ($Z$): This represents the number of protons in the nucleus of an atom.
    • Mass Number ($A$): This represents the total number of nucleons (the particles found inside the nucleus). Since protons and neutrons are the heavy particles that contribute significantly to the mass of an atom, their sum defines the mass number.

    The formula is:

    $\text{Mass Number (A)} = \text{Number of Protons (Z)} + \text{Number of Neutrons (N)}$

    Step-by-Step Solution

    1. Evaluate Option A: The mass number is always greater than or equal to the atomic number (because it includes neutrons), so this is incorrect.
    2. Evaluate Option B: As defined above, the mass number is the total count of protons and neutrons in the nucleus. This matches the scientific definition perfectly.
    3. Evaluate Option C: The mass number is an integer (a whole number), while atomic weight is often a decimal value representing the weighted average of isotopes. They are not directly related in this way.
    4. Evaluate Option D: The mass number is always a whole number because you cannot have a fraction of a proton or a neutron.

    Conclusion

    The mass number is defined as the sum of protons and neutrons in the nucleus. Therefore, option B is the correct definition.

    Exam Tip: Remember the acronym "MAN": Mass number = Atomic number + Neutrons. This will help you quickly calculate the number of neutrons if you are given the mass number and atomic number in a JAMB question!

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38. 38.

    The maximum electron in N shell is?

    1. A.2
    2. B.8
    3. C.18
    4. D.32

    Show answer

    Answer: D. 32

    AI explanation

    Analysis

    The question asks for the maximum number of electrons that can be accommodated in the N shell of an atom.

    Concept: The Bohr-Bury Rule

    In atomic structure, electrons are arranged in shells (energy levels) designated by the principal quantum number, $n$. The maximum number of electrons that any shell can hold is determined by the formula: Maximum electrons = $2n^2$

    Where $n$ is the shell number:

    • K shell: $n = 1$
    • L shell: $n = 2$
    • M shell: $n = 3$
    • N shell: $n = 4$

    Step-by-Step Solution

    1. Identify the shell number ($n$): The shells follow the alphabetical order K, L, M, N... Therefore, the N shell is the 4th shell. • $n = 4$
    2. Apply the formula: Substitute $n = 4$ into the formula $2n^2$. • Maximum electrons = $2 \times (4)^2$
    3. Calculate the value: • $4^2 = 16$ • $2 \times 16 = 32$

    The N shell can hold a maximum of 32 electrons.

    Conclusion

    The calculation confirms that the N shell accommodates 32 electrons.

    Exam Tip: Remember the sequence of maximum electrons for the first four shells:

    • K (1st): 2
    • L (2nd): 8
    • M (3rd): 18
    • N (4th): 32 A quick way to remember this is to double the square of the shell number. You've got this!

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39. 39.

    The metal used to recover copper from a solution of copper sulphate is?

    1. A.Na
    2. B.Ag
    3. C.Hg
    4. D.Fe

    Show answer

    Answer: D. Fe

    AI explanation

    Analysis

    The question asks us to identify which metal can displace copper from a copper(II) sulphate solution. This is a classic question based on the Reactivity Series of Metals (also known as the Electrochemical Series).

    Concept: The Reactivity Series

    In chemistry, a more reactive metal can displace a less reactive metal from its salt solution. This is known as a displacement reaction.

    The Reactivity Series ranks metals based on their tendency to lose electrons (their reducing power). The order of some common metals is: K > Na > Ca > Mg > Al > Zn > Fe > Sn > Pb > (H) > Cu > Hg > Ag > Au

    For a metal to displace copper from a copper(II) sulphate solution ($CuSO_4$), the metal must be higher in the reactivity series than copper.

    Step-by-Step Solution

    1. Analyze the options: • A. Na (Sodium): Sodium is very reactive and would react violently with the water in the solution rather than simply displacing the copper. It is not used for this purpose. • B. Ag (Silver): Silver is below copper in the reactivity series. It cannot displace copper. • C. Hg (Mercury): Mercury is also below copper in the reactivity series. It cannot displace copper. • D. Fe (Iron): Iron is above copper in the reactivity series. Therefore, iron can displace copper from its solution.

    2. The Chemical Equation: When iron is added to copper(II) sulphate solution, the following reaction occurs: $$Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s)$$ The iron dissolves to form iron(II) sulphate, and the copper is deposited as a solid.

    Conclusion

    Since iron is more reactive than copper, it effectively displaces copper from the copper sulphate solution.

    Exam Tip

    Remember the mnemonic for the reactivity series: "Please Stop Calling Me A Zebra In Large Heavy Cages, Save Gold." (Potassium, Sodium, Calcium, Magnesium, Aluminium, Zinc, Iron, Lead, Hydrogen, Copper, Silver, Gold). Any metal to the left of another can displace it from its salt solution!

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40. 40.

    220g of carbon dioxide contains ----- moles

    1. A.5
    2. B.6
    3. C.3
    4. D.4

    Show answer

    Answer: A. 5

    AI explanation

    1. Analyze the question

    You are asked to calculate the number of moles in a given mass (220g) of carbon dioxide ($CO_2$). To solve this, we need the molar mass of the compound.

    2. Explain the concept

    The relationship between mass, molar mass, and the number of moles is given by the formula:

    $\text{Number of moles (n)} = \frac{\text{Mass (m)}}{\text{Molar Mass (M)}}$

    • Mass (m): The given weight of the substance (220g).
    • Molar Mass (M): The sum of the atomic masses of all atoms in the molecule. • Atomic mass of Carbon (C) = 12 • Atomic mass of Oxygen (O) = 16

    3. Show the solution

    Step 1: Calculate the Molar Mass of $CO_2$

    • $CO_2$ consists of 1 Carbon atom and 2 Oxygen atoms.
    • Molar Mass = $(1 \times 12) + (2 \times 16)$
    • Molar Mass = $12 + 32$
    • Molar Mass = 44 g/mol

    Step 2: Calculate the number of moles

    • Using the formula: $n = \frac{m}{M}$
    • $n = \frac{220}{44}$
    • $n = 5$

    4. Identify the answer

    The calculation gives us 5 moles. Comparing this to the options provided: A. 5 B. 6 C. 3 D. 4

    The correct option is A.

    5. Exam Tip

    When dealing with molar mass questions in JAMB, always remember the atomic masses of common elements like Carbon (12), Oxygen (16), Hydrogen (1), and Nitrogen (14). If you can quickly sum these up, you save precious time during the exam! Also, ensure your units are consistent (grams to grams) before dividing.

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