Period: 1st (k-shell)
The only orbital of the s-subshell can accommodate a maximum of two electrons; the first period (k-shell) is exhausted by hydrogen (1 electron) and helium (2 electrons).
The only orbital of the s-subshell can accommodate a maximum of two electrons; the first period (k-shell) is exhausted by hydrogen (1 electron) and helium (2 electrons).