Epsom salts, which are effective in reducing swelling, are a hydrate of which compound?

Epsom salts are indeed a hydrate of magnesium sulfate. The chemical formula for Epsom salts is MgSO₄·7H₂O, indicating that each formula unit of magnesium sulfate is associated with seven water molecules, forming a crystalline structure that characterizes the hydrate. This compound is well-known for its therapeutic properties, especially in baths to relieve muscle soreness and reduce swelling due to the magnesium ions and sulfate ions it releases when dissolved in water.

The other compounds listed do not form similar hydrates or possess the same therapeutic applications. Magnesium chloride, magnesium hydroxide, and magnesium carbonate each have different properties and uses, making magnesium sulfate the unique compound associated with Epsom salts.