Question

Which is a pair of isotones?

Options

• ₁₁Na²³ and ₁₂Mg²⁴

• ₇N¹⁵ and ₇N¹⁴

• ₁₇Cl³⁵ and ₁₇C1³⁷

• ₂₀Ca⁴⁰ and ₁₈Ar⁴⁰

Answer 1

₁₁Na²³ and ₁₂Mg²⁴

Explanation:

₁₁Na²³ has Z = 11 and N = 23 − 11 = 12

₁₂Mg²⁴ has Z = 12 and N = 24 − 12 = 12

Both have 12 neutrons, so they are isotones.

The other pairs are isotopes or isobars.