An atom with a mass number of 234 and an atomic number of 90 has?

A. 90 neutrons and 144 protons

B. 234 neutrons and 90 protons

C. 144 neutrons and 90 protons

D. 117 neutrons and 117 protons

The answer is C. An atom consists of neutrons and protons. The atomic number is equals protons number. So, the proton number is 90. The proton and nuetron can both count for 1. So the mass number equals protons plus neutrons. The neutrons is 234 - 90 = 144.