One mole of a symmetrical alkene on ozonolysis gives two moles of an aldehyde having a molecular mass of $44\mathrm{u}.$ The alkene is:

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: