WHAT IS THE DIFFERENCE BETWEEN MASS NO. AND ATOMIC WEIGHT OF AN ATOM?

The number of protons in the nucleus of an atom determines an element's atomic number. In other words, each element has a unique number that identifies how many protons are in one atom of that element.

The mass number (A), also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus. It determines the atomic mass of atoms.