Which of the following salts does not contain water of crystallization?
(a) Blue vitriol
(b) Baking soda
(c) Washing soda
(d) Gypsum

The chemical formula of the given chemical compounds are:
Baking soda: ${\text{NaHCO}}_3$
Blue vitriol: ${\text{CuSO}}_4.5{\text{H}}_2\text{O}$
Washing soda: ${\text{Na}}_2{\text{CO}}_3.10{\text{H}}_2\text{O}$ and
Gypsum: ${\text{CaSO}}_4.2{\text{H}}_2\text{O}$.

So, baking soda does not contain water of crystallization.