The correct answer is 'X' is aluminium hydroxide; 'Y' is sulphuric acid.Concept:Acids:They are sour in taste.They turn blue litmus red. Its pH value ranges from 1 to 7 on the pH scale.Bases:They are bitter in taste and soapy to touch.They turn red litmus blue.Its pH value ranges from 7 to 14 on the pH scale.Explanation:Substance 'X' turns red litmus blue: It is a base. Substance 'Y' turns blue litmus red: It is an acid.Given: 'X' and 'Y' react with each other to form water and aluminium sulphate. X + Y ? H2O + Aluminium sulphate. Acid and base react together to form salt and water. 'X' is aluminium hydroxide; 'Y' is sulphuric acidPossible because X is base and y is acid.'X' is sulphuric acid; 'Y' is aluminium chlorideNot possible because X is a base'X' is sulphuric acid; 'Y' is aluminium hydroxideNot possible because X is a base'X' is aluminium; 'Y' is sulphuric acidNot possible because Aluminium is not a base, aluminium hydroxide is.