Question

The number
of
electrons is not
added while calculating the mass number of an element.​

Answer 1

Answer:

The small contribution of mass from electrons is disregarded in calculating the mass number. This approximation of mass can be used to easily calculate how many neutrons an element has by simply subtracting the number of protons from the mass number. Protons and neutrons both weigh about one atomic mass unit or amu.

Answer 2

Answer:

since the mass of an electron is 1/2,000th of the mass of proton any contributing that electrons make overall mass of an atom is negligible . therefore the number of electrons present in an atom are ignored when calculating the mass number of that atom