Phenylacetylene on treatment with `HgSO_(4)//H_(2)SO_(4), H_(2)O` produces

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

Acetylene when treated with dil. H_(2)SO_(4) and HgSO_(4) given

When 2-pentyn is treated with dilute H_(2)SO_(4) and HgSO_(4) the product formed is

When 1-butyne undergoes oxymercuraction with the help of HgSO_(4)+H_(2)SO_(4) , the product(s) formed is/are