Question

How is the mass number related to the number of protons and neutrons an atom has?

Answer 1

The mass number of an individual atom is the sum of the protons and the neutrons.

Explanation:

The proton has a mass of approximately 1 amu
The neutron has a mass of approximately 1 amu
The electron has a mass of several orders of magnitude less than 1 amu. The mass of the electrons can be ignored when calculating the total mass of the atom.

`p + n = mass`