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

(a)

(b)

(c)

The reaction is a acid base reaction.

Thus, after the donation of the OH^- ion formation of benzyl carbocation takes place.

When an electron-withdrawing group (NO₂, Cl) is present on the aromatic ring the carbocation stability decreases.Since the electron-withdrawing property of NO₂ is greater than Cl, the carbocation will be highly unstable.

Thus, an order of reactivity is b<c<a in increasing order.