What is a characteristic of hydrophobic substances?

Hydrophobic substances are characterized by their lack of affinity for water, which is primarily due to their nonpolar nature. These substances do not readily interact with water molecules, which are polar. The absence of attraction to water means that hydrophobic substances tend to aggregate together to minimize their exposure to the polar environment. This behavior is a fundamental principle in biology, affecting the structures of cell membranes and protein folding, as nonpolar regions seek to avoid contact with water.

In the context of the other options, substances that are attracted to water typically contain polar covalent bonds (as suggested in one of the choices) or are able to dissolve in polar solvents. Since hydrophobic substances do not exhibit these properties, the focus on their lack of attraction to water is what defines their hydrophobic characteristic.