Question

1. which of the following represent isotopes? a. (ce{^{40}_{18}ar}) and (ce{^{40}_{20}ca}) b. (ce{^{12}_{6}c}) and (ce{^{13}_{6}c}) c. (ce{^{35}_{17}cl}) and (ce{^{80}_{35}br}) d. (ce{^{24}_{12}mg}) and (ce{^{12}_{6}c}) e. none of the above.

Explanation:

Isotopes have the same atomic number (same element) but different mass numbers.

• Option A: Different elements (Ar, Ca), different atomic numbers.
• Option B: Both are C (atomic number 6), different mass numbers (12, 13) → isotopes.
• Option C: Different elements (Cl, Br), different atomic numbers.
• Option D: Different elements (Mg, C), different atomic numbers.

Answer:

B. $\ce{_{6}^{12}C}$ and $\ce{_{6}^{13}C}$