The correct order of reactivity for the addition reaction of the given carbonyl compounds with ethylmagnesium iodide is $1>111>11>\mathrm{IV}$

This order can be explained on the basis of following two factors:
(i) Inductive effect Greater the number of alkyl (electron releasing) groups attached to carbonyl group, greater will be the electron density on carbonyl carbon. Thus, it lowers the attack of nucleophile and hence, reactivity decreases.
(ii) Steric effect As the number of alkyl group attached to carbonyl carbon increases, the attack of nucleophile on carbonyl group becomes more and more difficult due to steric hinderance.