CBSE Class 10 Science 2018 · Paper 31(B) · Question 6(b)

Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt; these molecules are part of the salt's crystals. Two salts (any two): 1. Magnesium sulphate heptahydrate (Epsom salt), ${\text{MgSO}}_4\cdot 7{\text{H}}_2\text{O}$ 2. Sodium sulphate decahydrate (Glauber's salt), ${\text{Na}}_2{\text{SO}}_4\cdot 10{\text{H}}_2\text{O}$ Other correct examples earn the marks equally, such as copper sulphate pentahydrate, ${\text{CuSO}}_4\cdot 5{\text{H}}_2\text{O}$, washing soda, ${\text{Na}}_2{\text{CO}}_3\cdot 10{\text{H}}_2\text{O}$, and gypsum, ${\text{CaSO}}_4\cdot 2{\text{H}}_2\text{O}$.