Which of the following is a characteristic of a polar solvent?

A polar solvent is characterized by its ability to mix with water, which is itself a polar substance. This solubility arises because polar solvents contain molecules that have a significant difference in electronegativity between the atoms, resulting in a dipole—an uneven distribution of electrical charge. This characteristic enables polar solvents to effectively interact with water molecules through hydrogen bonding and other polar interactions.

Hence, the ability of a polar solvent to mix with water is key in various chemical processes, particularly in solutions where polar substances are necessary. Polar solvents are commonly used in many applications where dissolving salts and other polar compounds is required, thus playing a critical role in both laboratory and industrial scenarios.

In contrast, other characteristics mentioned in the choices do not define polar solvents accurately; many do not mix with water, do not contain both polar and non-polar components, or may not be flammable. Therefore, the defining feature of polar solvents is their affinity for and ability to mix with water.