Question

1. Why do all atoms of an element have the same atomic number, although they may have different mass numbers?

Answer 1

Atoms of an element have the same atomic number but different mass numbers because the atomic number only contains the amount of protons in an element.
Atoms of the same element that have different mass numbers are called isotopes.
With (AZ)X, the A is the number of protons, the Z is the number of neutrons, and the X is the electrons.