Isotopes of Chlorine: Properties and Definitions

Steps:

• Isotopes are atoms of the same element with the same atomic number but different mass numbers.
• Chlorine's common isotopes are Cl-35 and Cl-37, both with 17 protons but 18 and 20 neutrons, respectively.
• Mass differences arise from varying neutron counts, affecting total mass and nucleons.
• Chemical properties depend on electron configuration, which is identical for isotopes.

Why A is correct:

• By definition, isotopes have the same atomic number but different mass numbers, so Cl-35 and Cl-37 have different atomic masses.

Why the others are wrong:

• B: Isotopes do have different numbers of nucleons (protons + neutrons), as neutron count varies; this statement is actually correct.
• C: Isotopes have the same chemical reactions due to identical electron configurations and atomic number.
• D: Not enough information, as option D is incomplete.

Final answer: Not enough information.