Answer:
MgSO4.7H2O
Explanation:
The heating removes all the water (H2O) in the crystal.
The mass of the water removed = 82-40.1 = 41.9 grams.
The formula of the hydrated salt = MgSO4. xH2O
The ratio in of the masses of MgSO4 : H2O = 40.1 : 41.9
Dividing these by the molar masses we get
40.1/ 120.4 to 41.9 / 18.016
= 0.33 : 2.33
= 1 : 7.
So there are 7 water molecules n the hydrate.
