Which of the following statements are TRUE of isotopes? I. Isotopes of an element have the same chemical…

To solve this question, let’s break down the definition and characteristics of isotopes.

1. Analyze the Concept

Isotopes are atoms of the same element that have the same number of protons (atomic number) but a different number of neutrons (mass number).

• Statement I: Chemical properties are determined by the arrangement of electrons in the outer shell of an atom. Since isotopes of the same element have the same number of protons, they must have the same number of electrons to remain neutral. Therefore, they exhibit identical chemical properties. (True)
• Statement II: Because isotopes have different masses (due to the difference in the number of neutrons), they have slightly different physical properties (such as density, rate of diffusion, or boiling point). These differences in physical properties are exactly what scientists exploit to separate them (e.g., using a mass spectrometer or gaseous diffusion). (True)
• Statement III: By definition, the identity of an element is determined by its proton number. If the number of protons were different, it would be a completely different element. Thus, all isotopes of a specific element must have the same number of protons. (True)

2. Step-by-Step Evaluation

• Statement I is correct: Same electrons = same chemical behavior.
• Statement II is correct: Physical separation methods (like mass spectrometry) rely on the mass difference between isotopes.
• Statement III is correct: The definition of an isotope requires the proton number to remain constant.

Since all three statements (I, II, and III) are scientifically accurate, the correct option must include all of them.

3. Conclusion

Exam Tip: When you see questions about isotopes, always remember the "P-E-N" rule:

• Protons: Same
• Electrons: Same
• Neutrons: Different This simple mnemonic will help you quickly identify the properties of isotopes in any exam setting.