# What is the correct term for atoms of a single element that possess different numbers of neutrons?

$\text{An isotope.............}$
The number of protons always defines the identity of the element inasmuch as it gives $Z$, the atomic number. The simplest atom, hydrogen, has a number of common isotopes, i.e. ""^1H, $\text{protium} ,$ ""^2H, $\text{deuterium} ,$ ""^3H, $\text{tritium} .$ What are the numbers of neutrons in each nucleus?