During the debromination of $meso$-dibromobutane, the major compound formed will be

In the following reaction sequence, structures of $\mathrm{A}$ and $\mathrm{B}$ are, respectively

Fill up the blank:

$\mathrm{NaOH}+{\mathrm{H}}_2\mathrm{S}\to$ _____$+{\mathrm{H}}_2\mathrm{O}$  (Give the name of the compound formed)

The major product of the following reaction is :

The major products of the following reaction are :

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

In the following reaction the major product is

Which of the following statements is not correct for a nucleophile?

The major product in the following reaction is :

Here, $\mathrm{Z}$ is: