Question

Which of the following configuration represent alkaline earth metal:

• A. $1s^{2}2s^{2}2p^2$
• B. $1s^{2}2s^{2}2p^{6}3s^1$
• C. $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{5}4s^{2}4p^6$
• D. $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{2}4p^{6}4d^{10}5s^{2}5p^{6}6s^2$

Answer 1

The correct option is D $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{2}4p^{6}4d^{10}5s^{2}5p^{6}6s^2$

Alkaline earth metals have two electrons in their valence shell and the last electron enters in s-subshell.
In the configuration,$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{2}4p^{6}4d^{10}5s^{2}5p^{6}6s^2$, the last electron enters the s-subshell and has 2 electrons as valence electrons.Therefore it represents an alkaline earth metal.