The correct answer is MgSO₄.7H₂O.
The hydrate of magnesium sulfate goes through dehydration due to action of heat. This procedure can be represented chemically as follows:
MgSO₄.XH₂O (5.018 g) = MgSO₄ (2.449 g) + XH₂O (2.569 g)
The number of moles of H2O evolved = 2.569 / molecular weight
= 2.569 / 18 = 0.1427
Number of moles of MgSO₄ produced after decomposition,
= 2.449 / molecular weight
= 2.449 / 120.37
= 0.0203
Now dividing both these numbers to obtain the mole ratio, which prevails between MgSO₄ and H₂O
For H2O = 0.1427 / 0.0203 = 7.02 or 7
Therefore, the formula for the hydrate is MgSO₄.7H₂O.