Which of the following molecule does not obey the octet rule and also has lone pair electrons on the central atom?

detailed solution

Correct option is D

Atomic number of sulphur (S), Z = 16 and its electron configuration is 

$\left[\mathrm{Ne}\right]3s^{2}3p^2 {}_{x}3p_y{}^{1}3p_z^1$

In first excited state, one of the 3p electrons promoted into 3d orbital.

Now, sulphur has four unpaired electrons of its valence shell. Then the four Cl atoms with unpaired electrons are combined with sulphur atom forms ${\mathrm{SCl}}_4$ .The structure of ${\mathrm{SCl}}_4$  is shown as below.

The central atom “sulphur S” has one lone pair electrons. Therefore, ${\mathrm{SCl}}_4$ does not obey the octet rule, because sulphur has total 10 electrons (8 bonding and 2 non bonding electrons).

Note: The remaining three molecules are following “octet rule”.