Question

Which compound will react faster with OH and why???

Answer 1

In the SN2 mechanism, the reactivity of halides for the same alkyl group increases in the order. This happens because as the size increases, the halide ion becomes a better leaving group.
R−F << R−Cl < R−Br < R−I
Therefore, CH3I will react faster than CH3Br in SN2 reactions with OH.

Answer 2

compound having 2 cl group attached will react faster because it's forming carbonation having aromaticity thus making it more stable.