Write the ${\mathrm{S}}_{\mathrm{N}}2$ mechanism for the conversion of methyl chloride to methyl alcohol.

KI in acetone, undergoes S_N2 reaction with each of P, Q, R and S. The rates of the reaction vary as

The major product of the following reaction is

Represent the union of two sets by Venn diagram for each of the following.

$X=\{x | x$ is a prime number between $80$ and $100\}$

$Y=\{y | y$ is an odd number between $90$ and $100\}$