Question

which of the following best represents a pair of isotopes?
carbon-12 and oxygen-12
carbon-12 and $^{24}_{14}mg$
carbon-12 and carbon-14
$^{6}_{12}x$ and $^{12}_{6}x$

Explanation:

Isotopes are atoms of the same element with different mass - numbers due to different numbers of neutrons. Carbon - 12 and Carbon - 14 are both carbon atoms with mass numbers 12 and 14 respectively. The other pairs involve different elements or incorrect notations.

Answer:

Carbon-12 and Carbon-14