The alkane which is next to methane in homologous series can be prepared from which of the following reactions?

$ \text { I. } 2 \mathrm{CH}_{3} \mathrm{Br} \xrightarrow[\text { Dry ether }]{\mathrm{Na}} $

II. $\mathrm{CH}_{3} \mathrm{COOH} \xrightarrow[\mathrm{CaO}, \Delta]{\mathrm{NaOH}}$

III. $\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CH}_{2} \xrightarrow{\mathrm{H}_{2} / \mathrm{Pt}}$ IV. $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Br} \xrightarrow[\mathrm{H}^{+}]{\mathrm{Zn}}$

What is ' $ Y $ ' in the following set of reactions?

$$ \mathrm{C}_3 \mathrm{H}_4 \xrightarrow[\substack{\mathrm{Hg}^{2+} / \mathrm{H}^{+} \\ 333 \mathrm{~K}}]{\mathrm{H}_2 \mathrm{O}} X \xleftarrow[\substack{\text { (ii) } \mathrm{Zn}+\mathrm{H}_2 \mathrm{O}}]{\text { (i) } \mathrm{O}_3} Y $$