The rate of the reaction

is influenced by the hyperconjugation effect of group R. If R is sequentially
`CH_(3)^(-)` (II) `CH_(3)-CH_(2)`
(III) `CH_(3)-underset(CH_(3))underset(|)CH-` , (IV) `H_(3)C-overset(CH_(3))overset(|)underset(CH_(3))underset(|)C-`
the increasing order of speed of above reaction is

Options

A. IV,III,II,I
B. I,II,III,IV
C. I,IV,III,II
D. III,II,I,IV

Answer

B

Explanation

More the number of H atoms on the `alpha` carbon of the group R, more are the hyper conjugation structures, weaker is the C-B bond and hence higher is the rate of reaction.
Now since `CH_(3)` has three, ethyl has two, iso- propyl has one and tert butyl group has no `alpha`-hydrogen, therefore, hyper conjugation effect decreases and hence the rate decreases in the same order (B), is correct