# What is the difference between individual isotoples of the same element?

These differ in the number of $\text{neutrons...........}$
These differ in the number of $\text{neutrons}$, massive, NEUTRAL, $\text{nucular}$ particles.
If the particles are isotopes of the same element, then by definition their nuclei contain equal numbers of protons, massive, positively charged nuclear particles. The nuclei, however, contain different numbers of neutrons, massive, neutral nuclear particles. Hydrogen, the simplest element, has a few isotopes available, $\text{^1H, "protium}$, $\text{^2H, "deuterium}$, $\text{^3H, "tritium}$. How many neutrons reside in each isotope?