Hydration of in presence of `H_(2)SO_(4) // HgSO_(4)` gives `(` as a major product `)`

Action of acetylene on dilute H_(2)SO_(4)//dil. HgSO_(4) gives:

Addition of water to ethyne in the presence of H_2SO_4 and HgSO_4 gives

Hydroxylation of propyne in the presence of HgSO_(4)//H_(2)SO_(4) is initiated by the attack of :

Acetylene on treatment with dil. H_(2)SO_(4) having HgSO_(4) gives:

When but-1-yne is treated with aqueous H_(2)SO_(4) in presence of HgSO_(4) , the major product is __________.