2 protons, 2 electrons, 1 neutron
Work Step by Step
Helium has an atomic number of 2 (it is number 2 on the periodic table), therefore it has 2 protons. The mass number given on 3He is 3, which is the number of protons + neutrons. Therefore, if it has 2 protons then 3-2 = 1 neutron. Finally, it is not charged so the positive charges (protons) must balance the negative charges (electrons). Thus, we have 2 electrons.