As has an atomic number of 33, so it has 33 protons.
It has a charge of 3-, so there are three more electrons than protons. Thus, there are 36 electrons.
It has a mass of 75, which is the sum of neutrons and protons.
33+n=75 ---> n = 75 - 33 = 42 neutrons
The answer is e) 33 protons, 42 neutrons and 36 electrons.
