What properties make a substance hydrophilic?

A substance is considered hydrophilic when it has an affinity for water, meaning it can interact well with water molecules. The defining property of a hydrophilic substance is its ability to mix easily with water. This quality is often due to the presence of polar groups or ions within the substance that can form hydrogen bonds with water. Such interactions increase solubility and allow hydrophilic substances to disperse in water, thereby creating solutions.

In contrast to hydrophilic substances, those that repel water do not create favorable interactions with water molecules and tend to separate from them. High surface tension is typically associated with liquids like water itself rather than being a characteristic of a hydrophilic substance. Finally, a hydrophilic substance would absorb moisture rather than absorb very little, as its fundamental nature allows it to attract and hold onto water. Thus, the ability to mix easily with water is what fundamentally characterizes a substance as hydrophilic.