The Pauli exclusion principle states that:
(a) No two electrons in an atom can have the same spin.
(b) No two electrons in an atom can occupy the same orbital.
(c) Two electrons in the same orbital have identical values of the spin quantum number.
(d) No two electrons in an atom can have the same set of four quantum numbers.
(e) Electrons in a subshell are arranged to maximize the total amount of spin.
Answer: (d) No two electrons in an atom can have the same set of four quantum numbers.