400
How many protons, neutrons, and electrons are present in an atom of hafnium, Hf, with a mass number of 178?
A 72 protons, 178 neutrons, 106 electrons
B 72 protons, 106 neutrons, 72 electrons
C 178 protons, 250 neutrons, 72 electrons
D 106 protons, 72 neutrons, 106 electrons
B 72 protons, 106 neutrons, 72 electrons