Understanding Viscosity Variation with Temperature

The question asks us to evaluate two statements concerning how the viscosity of liquids and gases changes with temperature. Let's break down each statement.

Statement A: Viscosity of Liquids and Temperature

Statement A suggests that the viscosity of liquids decreases as the temperature increases. This is generally true for liquids.

Explanation:

• Viscosity in liquids is primarily caused by the cohesive forces between molecules. These forces resist the relative motion of fluid layers.
• As the temperature of a liquid rises, its molecules gain more kinetic energy. This increased energy allows the molecules to overcome the intermolecular cohesive forces more easily.
• When these forces are weakened, the internal resistance to flow (viscosity) decreases.
• Think of honey: it's very viscous when cold, but it flows much more easily when warmed up.

Therefore, Statement A is correct.

Statement B: Viscosity of Gases and Temperature

Statement B suggests that the viscosity of gases decreases as the temperature increases. This is generally incorrect for gases.

Explanation:

• In gases, viscosity arises mainly from the transfer of molecular momentum between adjacent layers. Faster-moving molecules from one layer collide with slower-moving molecules in another, transferring momentum and creating resistance to flow.
• When the temperature of a gas increases, its molecules move faster and collide more frequently.
• This increased molecular motion and collision rate leads to a greater transfer of momentum between layers.
• Consequently, the resistance to flow, or viscosity, increases with increasing temperature in gases.

Therefore, Statement B is incorrect.

Conclusion on Statements

Based on the analysis:

• Statement A is correct: Liquid viscosity decreases with increasing temperature.
• Statement B is incorrect: Gas viscosity increases with increasing temperature.

The correct option is the one that identifies Statement A as correct and Statement B as incorrect.