Which of the following undergoes hydrolysis most easily

What is the type of following reaction?

Consider the following alcohols:

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

Predict the product formed in the following reaction:

What is compound $\mathrm{Z}$?

${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CH}}_2\mathrm{Br}\stackrel{\mathrm{NaCN}}{\to }\mathrm{X} \underset{\mathrm{heat}}{\overset{{\mathrm{H}}_3{\mathrm{O}}^{+}}{\to }}\mathrm{Y} \underset{{\mathrm{H}}^{+}}{\overset{{\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}}{\to }} \mathrm{Z}$