Phenol can be distinguished from ethanol by the reaction with

Arrange the following compound in decreasing order of reactivity in ${\mathrm{SN}}^2$ reaction.

(a) 

(b) ${\mathrm{CH}}_3-{\mathrm{CH}}_2-{\mathrm{CH}}_2-{\mathrm{CH}}_2\mathrm{Br}$

(c) 

(d) 

In the following reaction :

${\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{CH}}_2\mathrm{Br}\underset{2{\mathrm{H}}_3{\mathrm{O}}^{+}}{\overset{1.\text{Mg.Ether }}{\to }}\mathrm{X}$, the product $\text{'}\mathrm{X}\text{'}$ is :

What is major product $\left(\mathrm{X}\right)$ :-