Name a chemical reaction which is characteristic of unsaturated hydrocarbons (like alkenes and alkynes).

44 An organic compound X of molecular formula C₂H₄O₂ gives brisk effervescence with sodium hydrogencarbonate. Give the name and formula of X. 44 A mixture of ethyne (acetylene) and oxygen is burnt for welding. Can you tell why a mixture of ethyne and air is not used? 45 What is meant by an addition reaction? Give an example (with equation) of an addition reaction of an alkene. 45 What is added to groundnut oil when it is to be converted to vanaspati ghee?