Which one of the following compound is least reactive towards $\mathrm{EtO}-/\mathrm{EtOH}?$

possible product is/ are:

The above reaction is example of:

Consider the following alcohols:

The order of decreasing reactivities of these alcohols towards nucleophilic substitution with $\mathrm{HBr}$ is:

The correct order of ${\mathrm{S}}_{\mathrm{N}}2/\mathrm{E}2$ ratio for the$\%$ yield of product of the following halides is:

(P)  ${\mathrm{CH}}_2-{\mathrm{CH}}_2-\underset{\mathrm{I}}{\overset{\mathrm{Ph}}{\underset{\left|}{\overset{\right|}{\mathrm{C}}}}}-{\mathrm{CH}}_3$ 

(Q) ${\mathrm{CH}}_3-\underset{\mathrm{Ph}}{\underset{|}{\mathrm{CH}}}-\underset{\mathrm{I}}{\underset{|}{\mathrm{CH}}}-{\mathrm{CH}}_3$

(R) ${\mathrm{CH}}_3-{\mathrm{CH}}_2-\mathrm{I}$ 

(s) ${\mathrm{CH}}_2-\mathrm{CH}-\underset{\mathrm{I}}{\underset{|}{\mathrm{CH}}}-{\mathrm{CH}}_2$