`underset("Ethyne")underset()(CHequivCH)overset("dil.H_(2)SO_(4))underset(HgSO_(4))rarrunderset(Ethanal (A))underset()(CH_(3)CHO)overset(dil.NaOH)rarrunderset(Aldol(B))underset()(CH_(3)CH(OH)CH_(2)CHO)overset(heat)underset(-H_(2)O)rarrunderset(But-2-enal(C))underset()(CH_(3)CH=CHCHO`