What describes the degree to which a substance will mix with water?

The term that describes the degree to which a substance will mix with water is water solubility. This concept is essential in understanding chemical behaviors, especially in hazardous materials response, as it directly affects how a material may behave if it spills or comes into contact with water. A substance that is highly soluble in water will dissolve readily and can spread quickly in aqueous environments, potentially leading to more significant hazards, such as toxicity to aquatic life or the formation of harmful concentrations.

Other terms listed, while relevant in their contexts, do not specifically define the mixing ability with water. Water reactivity refers to how a substance might chemically react with water, which is different from simply mixing. Water toxicity is concerned with the harmful effects of a substance on living organisms when dissolved in water, rather than the mixing process itself. Water compatibility relates to how well a substance can coexist with water without causing adverse reactions, but again, it does not specifically refer to the degree of mixing. Therefore, water solubility is the accurate choice for describing how well a substance dissolves in water.