(i) Hydrated salt is a salt with water as water of crystallisation whereas Anhydrous salt is the salt which gives away its water of crystallisation.
(ii) Washing soda is sodium carbonate having ten molecules of water of crystallisation (Na2CO3⋅10H2O) where- as soda ash is sodium carbonate decahydrate (Na2CO3⋅10H2O) when it loses its 9 units of crystallisation it is called soda ash (Na2CO3⋅H2O).
(iii) Baking soda is sodium bicarbonate (NaHCO3) whereas baking powder is a mixture of baking soda (NaHCO3) and tartaric acid (C4H6O6).