Which of the following salts does not contain water of crystallisation?
Blue vitriol
Baking soda
Washing soda
Gypsum
Steps: Baking soda = NaHCO₃ (typically anhydrous). Blue vitriol = CuSO₄·5H₂O, washing soda = Na₂CO₃·10H₂O, gypsum = CaSO₄·2H₂O. So baking soda does not contain water of crystallisation.