The mass number of an atom is the same as?
A. the protons it contains.
B. the neutrons it contains.
C. the number of protons and neutrons it contains.
D. the number of protons and electrons it contains.

Option C.

The number of protons and neurons it's contain.

Explanation:

Mass number of an atom is also called atomic mass of an atom which is some what expressed in Dalton i.e 1/2. The mass number is the total number of protons and neutrons altogether called nucleons in an atomic nucleus.

your answer is rna to the question.