13.57 g of hydrate magnesium sulfate is heated, leaving behind a residue of 6.63 g. What are the name and formula of this hydrated salt?
a. Magnesium sulfate heptahydrate, MgSO₄·7H₂O
b. Magnesium sulfate pentahydrate, MgSO₄·5H₂O
c. Magnesium sulfate tetrahydrate, MgSO₄·4H₂O
d. Magnesium sulfate monohydrate, MgSO₄·H₂O