Rate of reaction with HBr Rate of reaction is more when Carbon is more electrophile(less electron density)

So according to me the order should be D>B>C>A

As NO2 has -M -I effect , Cl has +M -I effect , while OCH3 has +M -I effect.

But the answer given as A>B>C>D
Stability of carbocation is directly proportional to +M effect .
So ,
 carbocation will more stable on A then on B and then C as NO2 has high -M. Effect it's last..