How does temperature affect viscosity?

• A. Liquid temperature increases - viscosity decreases; Gas temperature increases - viscosity increases
• B. Viscosity is unaffected by temperature
• C. Both liquids and gases viscosity increase with temperature
• D. Liquids viscosity increase with temperature; Gases viscosity decrease with temperature

Answer: (A)

Temperature changes viscosity differently in liquids and gases because viscosity comes from how the molecules interact and transfer momentum in each phase.

In liquids, heating reduces intermolecular forces and lets molecules move more freely, so layers slide past each other with less resistance. That lowers viscosity as temperature rises.

In gases, higher temperature increases molecular speeds and enhances momentum transfer between layers during collisions, which makes the gas resist shear more and raises viscosity with temperature.

So, as temperature increases: liquids become less viscous, gases become more viscous. This matches the idea that liquids’ viscosity decreases with temperature while gases’ viscosity increases with temperature. The other statements don’t fit what actually happens: viscosity isn’t temperature‑independent; it’s not that both phases increase; and it’s not liquids increasing while gases decrease.