Answer: B. \(\text{MgSO}_4\) is soluble in water; sand is not. Adding water dissolves the magnesium sulfate, and filtering separates the sand. Heating during dissolution isn't needed at room temperature.
The filtrate must then be evaporated to saturation and cooled — not to dryness. Magnesium sulfate crystallises as a hydrate (\(\text{MgSO}_4 \cdot 7\text{H}_2\text{O}\)). Evaporating to dryness drives off the water of crystallisation and destroys the hydrated crystal structure, leaving an anhydrous powder rather than the proper crystals.
Options A and C evaporate to dryness. Option D unnecessarily heats during dissolution.
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