Which term describes the ability of a drug to move freely in water?

The term that describes the ability of a drug to move freely in water is hydrophilic. A hydrophilic substance has an affinity for water, meaning it can easily dissolve in or interact with water. This property is crucial for many drugs, as their effectiveness can depend on their solubility in biological fluids, which are primarily composed of water. When a drug is hydrophilic, it can be absorbed and transported through the bloodstream effectively, allowing it to reach its target sites in the body.

In contrast, lipophilic refers to substances that are attracted to or can dissolve in fats, whereas hydrophobic indicates a lack of affinity for water, meaning such substances do not dissolve in water well. Hydrophobicity is a measure of how hydrophobic a substance is, but it does not describe the ability to move freely in water. Therefore, hydrophilic accurately captures the concept of a substance that can move and dissolve easily in aqueous environments.