Which is the best reagent to convert cyclohexanol into cyclohexene.

The expected order of the boiling points of $\mathrm{I} - \mathrm{IV}$ would be:

In the following reaction sequence, $\mathrm{X}$ and $\mathrm{Y}$, respectively, are:

Reaction of $2$-butene with acidic ${\mathrm{KMnO}}_4$ gives:

The major product of the reaction is: