The correct option is
B (c)>(a)>(b)Reaction with
HBr takes place through carbocation intermediate formation.
More the stability of intermediate formed, more is the rate of reaction.
Intermediates formed are :
Intermediates (a) and (c) are stabilized by
+M effect , whereas (b) is only stabilized by hyperconjugation.
So (b) is the least stable
Since electronegativity of oxygen is more than that of nitrogen,
N will have a higher tendency to donate electrons as compared to
O.
So, carbocation is more stable in case of (c) as comapred to (a)
Order of intermediate stability :
(c)>(a)>(b) Rate of reaction order :
(c)>(a)>(b)