The state of a system is completely described by a complete set of quantum numbers. This set is written as (n, l, ml, ms). The Pauli exclusion principle says that no two electrons can have the same se...The state of a system is completely described by a complete set of quantum numbers. This set is written as (n, l, ml, ms). The Pauli exclusion principle says that no two electrons can have the same set of quantum numbers; that is, no two electrons can be in the same state. This exclusion limits the number of electrons in atomic shells and subshells. Each value of n corresponds to a shell, and each value of l corresponds to a subshell.