Which of the following bonds makes a hydrocarbon most reactive?

The reagent used for converting acetylene to oxalic acid is

The hydration of propyne results in the formation of:

What is the major organic product of the following reaction?
$Ph-C \equiv CH \xrightarrow[H_2SO_4]{Hg^{2+}, H_2O} ?$

Which of the following gases,when passed through a warm dilute solution of $H_2SO_4$ in the presence of $HgSO_4$,gives acetaldehyde?

Give the industrial preparation method of ethyne.