If an atom has 34 protons and 40 neutrons, the mass number is 74.
Explanation:
Mass number is related to the protons and neutrons. It is the product of the above two subatomic particles. Hence the mass number and the atomic number are dependent upon the subatomic particles of an atom. From the given data in the question, mass number of the atom is calculated as, 34 + 40 = 74.
