What characterizes an anhydrous compound?

An anhydrous compound is characterized by the absence of water, specifically lacking waters of crystallization. These compounds do not contain water molecules within their structure, which distinguishes them from hydrated compounds that have water integrated into their crystalline framework. For instance, copper(II) sulfate pentahydrate contains five water molecules associated with each formula unit, while anhydrous copper(II) sulfate does not have any water molecules connected to it.

The other aspects mentioned in the choices do not accurately reflect the nature of anhydrous compounds; they either describe hydrated forms or involve characteristics not intrinsic to the definition of anhydrous states. Therefore, identifying an anhydrous compound fundamentally relies on recognizing its lack of water in its composition.