A carbon compound $\mathrm{X}$ forms $\mathrm{Y}$with sodium metal. It also forms$\mathrm{Z}$ with ${\mathrm{PCl}}_5$, but $\mathrm{Y}$ and $\mathrm{Z}$ react to form diethyl ether. Therefore, $\mathrm{X}, \mathrm{Y} \mathrm{and} \mathrm{Z}$ are respectively.

When ethyl alcohol (${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}$) reacts with thionyl chloride, in the presence of pyridine, the product obtained is ______.

Which one is the Swarts reaction from the following?

The decreasing order of reactivity of the following compounds in ${\text{S}}_{\text{N}}\text{1}$ reactions is ______.

$$\begin{gathered} {\text{C}}_{\text{6}}{\text{H}}_{\text{5}}{\text{CH}}_{\text{2}}{\text{Br C}}_{\text{6}}{\text{H}}_{\text{5}}{\text{CH(C}}_{\text{6}}{\text{H}}_{\text{5}}\text{)Br} \\ \text{(i) (ii)} \\ {\text{C}}_{\text{6}}{\text{H}}_{\text{5}}{\text{CH(CH}}_{\text{3}}{\text{)Br C}}_{\text{6}}{\text{H}}_{\text{5}}{\text{C(CH}}_{\text{3}}{\text{) (C}}_{\text{6}}{\text{H}}_{\text{5}}\text{)Br} \\ \text{(iii) (iv)} \end{gathered}$$

Which of the following undergoes nucleophilic substitution by ${\mathrm{S}}_{\mathrm{N}}1$ mechanism?