Question

the mass number for an atom is numerically equal to which quantity?
a the number of protons plus the number of electrons plus the number of neutrons
b the number of protons plus the number of neutrons
c the number of neutrons only
d the number of protons plus the number of electrons

Explanation:

The mass number of an atom is defined as the sum of the number of protons and neutrons in the nucleus of the atom. Electrons have negligible mass compared to protons and neutrons and are not included in the calculation of the mass number.

Answer:

B. the number of protons plus the number of neutrons