Why do the elements with d subshell electrons not appear until the fourth row, even though there is a d subshell for n=3?
O Electrons in the d subshell do not have noticeable chemical activity for n=3.
O The d subshell is at higher energy than the s subshell with the next-higher value of n.
O Pauli's exclusion principle does not allow electrons into the d subshell for n = 3.
O Since the first row actually corresponds to n = 0 it follows that the fourth row is the correct place for the d subshell with n = 3.
