PAUL’S Exclusion Principle

Wolfgaug Pauli put forward the principle which restricts certain values of quantum numbers for an electron in an atom and hence the name exclusion principle. The principle states, “No two electrons in an atom can have the same set of four quantum numbers ( n, l, m, s ). For example, In ‘1s’ orbital (n = 1), according to Pauli’s Exclusion Principle there are only two possible arrangements of quantum numbers possible, i.e.
n =1, l = 0, m = 0, s = +½ ( 1st electron )
n =1, l = 0, m = 0, s = -½ ( 2nd electron )
This follows that a maximum of only two electrons can be accommodated in an orbital and they must possess opposite spins.