How many protons, electrons, and neutrons does an atom with atomic number 50 and mass number 125 contain?
a. 75 electrons, 50 protons, 50 neutrons
b. 120 neutrons, 50 protons, 75 electrons
c. 70 neutrons, 75 protons, 50 electrons
d. 50 protons, 50 electrons, 75 neutrons
