Which compound in the following pairs will react faster in `S_N^(2)` reaction?
(a). `CH_(3)Br` or `CH_(3)I`
(b). `(CH_(3))_(3)C Cl` or `CH_(3)Cl`

Explanation

(i) `CH_(3)I`alkyl iodides are more reactive than alkyl bromides because of the decreased strength of the carbon iodided bond
(ii)`CH_(3)CI` Tertiary haliders are very insert to `S_(N)2` reaction because they have too much steric bulk for efficient backside attack