What is the main property of molecules with polar functional groups in water?

Molecules with polar functional groups in water are characterized by their ability to interact favorably with water. This interaction arises from the polar nature of the functional groups, which allows them to form hydrogen bonds with water molecules. Such interactions increase the solubility of these molecules in water, as they can effectively disrupt the hydrogen-bonded network of water, leading to the mixing of polar substances with the solvent.

When polar groups, such as hydroxyl (-OH), carboxyl (-COOH), or amino (-NH2) groups, are present, they enhance the molecule's affinity for water, making these compounds hydrophilic. This is essential in biochemistry, where many biologically active molecules, such as proteins and sugars, possess polar groups that enable them to dissolve in the aqueous environments of cells.

The other options do not accurately represent the behavior of polar functional groups in water. For instance, polar molecules do have a capacity to form hydrogen bonds, they are often soluble in water rather than having limited solubility, and they are decidedly hydrophilic rather than hydrophobic.