If a solid is hydrated, which term best describes its composition?

• A. It contains water of crystallization.
• B. It contains no water at all.
• C. It is a metallic oxide.
• D. It is a carbonated solid.

Answer: (A)

Hydrates have water molecules that are part of their crystal structure. When a solid is hydrated, its composition includes water of crystallization, the water bound within the lattice. This water is not just trapped on the surface; it is incorporated into the solid's structure and can be removed by heating to yield the anhydrous form. So the best description is that it contains water of crystallization. The other options don’t fit: no water would mean the solid is anhydrous; a metallic oxide describes a compound without mentioning bound water; a carbonated solid would involve carbonate, not water bound in the crystal.