The correct answer is B. Isotopes
Step-by-step explanation:
Chemical elements are defined according to their proton number (particles positively charged), for example, in hydrogen, the atomic number is 1. Also, atoms of the same element usually have the same number of electrons (particles negatively charged) if the atom is neutral.
However, atoms of the same element can differ in the number of neutrons and therefore there are atoms with the same number of protons and electrons but not the same number of neutrons, these are known as isotopes. This variety in neutrons affects the properties of the atom such as reactivity. For example, hydrogen has three isotopes: tritium, deuterium, and protium and form this tritium is the more radioactive.