Which property of a fluid is described by viscosity?

Viscosity is defined as the measure of a fluid's resistance to flow. This property relates to how thick or thin a fluid is; for instance, honey has a higher viscosity than water due to its thicker consistency, making it flow more slowly.

Understanding viscosity helps in various applications, such as in the transportation of liquids through pipes or understanding how substances interact in chemical reactions. The other properties listed, such as boiling point, density, and chemical reactivity, pertain to different characteristics of substances. Boiling point refers to the temperature at which a liquid turns to vapor, density is the mass per unit volume of a substance, and chemical reactivity describes how a substance interacts chemically with other substances. Each of these properties represents a distinct characteristic, separate from the fluid's ability to resist flow.