Which property describes a semisolid's resistance to flow?

• A. Density
• B. Osmolarity
• C. Viscosity
• D. Boiling point

Answer: (C)

Viscosity is the measure of a material’s resistance to flow. Semisolids have a structured network formed by thickening agents and polymers that makes them flow much more slowly than liquids. This high resistance to movement is what keeps an ointment, gel, or paste in place on the skin or another surface instead of running away. Density, osmolarity, and boiling point describe other properties (mass per volume, solute concentration effects, and the temperature at which a substance boils) and do not capture how easily the material deforms and flows under stress. In practice, the viscosity of a semisolid also influences how easily you can spread it: applying shear can briefly lower the apparent viscosity to allow spreading, after which the structure helps it regain its resistance to flow.