The answer to this question would be: B. electrons with opposite spins
Proton and neutron located in the middle of the atom called nucleus. They are not located in orbit like electrons. So the option A and C will out since there is no way this diagram involving the protons.
The electron has a negative charge and there are no such as oppositely charged electrons. The diagram is actually telling about the orbit of the electron. Electron will be paired with other electrons that will go in opposite spin
