Question

Which elements are having $2$ electrons in valence sub-shell?

Answer 1

$A,C$;

electronic configuration is

• $A-1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^2$

• $C-1s^{2}2s^{2}2p^{6}3s^{2}3p^2$