The alkyne shown is hydrated with $\mathrm{HgSO}{}_4$/$\mathrm{H}{}_2\mathrm{SO}{}_4$. Which structure is the product?

The compound shown is ethyne. Addition of water gives the enol vinyl alcohol, which tautomerises to ethanal. This is the only alkyne that gives an aldehyde by Markovnikov hydration, because both carbons are terminal. Ethanol would need the alkene, and propanone needs a carbon more.