Mark the correct increasing order of reactivity of the following compounds with HBr/HCl.

Options

A. `I lt II lt III`
B. `II lt I lt III`
C. `II lt III lt I`
D. `III lt II lt I`

Answer

C

Explanation

Reaction of the given compounds with HBr/HCl is a nucleophilic substitution reaction. It follows `S_(N)^(1)` mechanism. `S_(N)^(1)` mechanism depends upon the stability of carbocation.
Presence of electron withdrawing group decreases the stability of carbocation. In compound (II) and (III) EWG is present at para position.
Since, `-NO_(2)` group is a stronger EWG than -Cl. So, `NO_(2)-C_(6)H_(5)-overset(+)(C)H_(2)` carbocation will be less stable than `Cl-C_(6)H_(5)-overset(+)(C)H_(2)` carbocation.
Thus, the order of stability of carbocation is

Therefore, compound (II) is least reactive and correct option is (III).