What term describes the ability of a substance to mix with water?

The correct term that describes the ability of a substance to mix with water is solubility. This property refers to how well a substance can dissolve in a solvent, which in this case is water. Solubility is crucial in various fields, including chemistry, environmental science, and fire behavior, as it influences how different materials interact in aqueous environments. This property can affect how substances behave when they come into contact with water, such as during firefighting efforts, where understanding how chemicals dissolve can guide effective strategies for extinguishing fires.

Other terms provided, like viscosity, density, and concentration, describe different physical properties. Viscosity refers to a fluid's resistance to flow, density is the mass per unit volume of a substance, and concentration quantifies the amount of a substance in a given volume of mixture. These properties are important in their own contexts, but they do not specifically address the dissolution capability of a substance in water.