Which of the following species determines the chemical properties of an atom?

Step 1: Analyze the question The question asks which particle determines how an atom behaves chemically, that is, how it bonds, reacts, gains or loses electrons, and so on.

Step 2: Explain the concept Chemical reactions involve the outermost (valence) electrons. Atoms react by losing, gaining, or sharing these electrons to achieve a stable configuration. Therefore, the number and arrangement of electrons, especially in the outer shell, decide the chemical properties.

• Neutron: has no charge and affects only the mass of the atom (and isotope type). Isotopes of an element have the same chemical properties despite different neutron numbers.
• Proton: determines the atomic number and so the identity of the element. In a neutral atom, the number of electrons equals the number of protons, which is why protons are indirectly linked to chemical behavior. But it is the electrons that actually take part in reactions.
• Nucleus: contains the protons and neutrons. It is not involved in ordinary chemical reactions.
• Electron: the particle that takes part in bonding and reactions.

Step 3: Solution Chemical properties depend on the valence electron configuration, so the answer is the electron.

Answer: A. Electron

Tip: Remember, "Protons identify, electrons react." The proton number tells you which element it is, but the electrons determine how it behaves chemically. Also, isotopes have the same chemical properties because they have the same number of electrons.