Clarify the following expression s
a.atomic number
b.mass number
c.nucleus

Atomic number of a chemical element is the number of protons found in the nucleus of every atom of that element.

The mass number, also called atomic mass number or nucleon number, is the total number of protons and neutrons in an atomic nucleus.

The atomic nucleus is the small, dense region consisting of protons and neutrons at the center of an atom.