Question

mass number of an atom excludes the mass of an electron give reason

Answer 1

It so because ,the mass of electrons are negligible as compared to that of protons and neutrons, so for the sake of calculation we neglect the mass of electron.

Answer 2

The mass of an electron is negligible.

Mass of electron = 9.1 x 10⁻³¹ kg
Mass of proton = 1.67 x 10⁻²⁷ kg

Comparing the mass of proton and electron , it is found that mass of electron is negligible. Therefore it is ignored.

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