Question

The mass number of an atom is found by1) adding the number of protons and neutrons.2) adding the number of protons and electrons.3) subtracting the number of protons from the number of neutrons.4) subtracting the number of protons from the number of electrons.

Answer 1

The mass number of an atom is the sum of number of protons present in the nucleus and number of neutrons present in the same nucleus.

`M=\text{Protons}+\text{Neutrons}`

Thus, 1st option is the correct answer.