Question

atomic mass number is whole number why

Answer 1

The answer for this question is - Atomic mass is never an integer number for several reasons: Theatomic mass reported on a periodic table is the weighted average of all the naturally occuring isotopes. Being an average it would be most unlikely to be a whole number. The mass of an individual atom in atomic mass units is the mass relative to carbon-12.

Answer 2

because it counts the numbers of protons in atom