(i)→ (d) , (ii) →(a) , (iii)→(b) ,(iv) → (c)

In reaction (i) H₂O molecule added to alkene and formation of ethanol, which is a example of hydration reaction.

In reaction (ii) one H₂ molecule add with ethylene formation of ethane. The reaction where H₂ reacts with a compound in presence of Pd catalyst is called hydrogenation reaction.

In reaction (iii) Cl₂ molecule add to ethylene formation of dichloro compound. This type of halogen addition reactions are termed as halogenation reaction.

In reaction (iv) 3 ethyne molecule act as a monomer unit, which combine and forming cyclic benzene molecule. So, this type of reaction where joining of molecule and forming products is called polymerisation reaction.