Electron Configurations in Atoms
When one has two electrons, as in He or Li+, each electron is assigned a set of four quantum numbers, and the Pauli principle is invoked to keep things straight. The Pauli principle states that no two electrons can have the same quantum number set. One (at least) of the four quantum numbers must be different from that of the other electron.
He could have a state 1p5d, where one electron is in the n = 1 state, ? = 1, and the other is in the n=5, ? = 2 state. Again, nothing is indicated about the other quantum numbers.
However, if both electrons are in the n=1 state, and if both electrons are in the ? =0 state (which means they must have m? = 0) then ms one electron must be ? and the other ?