Answer
A. $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}$
Work Step by Step
A. $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}$ - electron configuration is that of an inert gas because of filled 3s and 3p subshells
B. $1s^{2}2s^{2}2p^{6}3s^{2}$ - electron configuration is that of an alkaline earth metal because of two s electrons
C. $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{1}$- electron configuration is that of an alkali metal because of a single s electron
D. $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{2}4s^{2}$ - electron configuration is that of a transition metal because of an incomplete d subshell
