Origin of viscosity in liquids — conceptual check The viscosity of a liquid primarily arises due to cohesion between its molecules. Is this statement correct?

Introduction / Context:
Viscosity is a measure of internal resistance to flow. Its microscopic origin differs between liquids and gases. Recognizing this difference helps explain why liquid viscosity generally decreases with temperature, while gas viscosity increases.

Given Data / Assumptions:

• Continuum fluid behavior is considered, with molecular interpretation for trends.
• Liquids possess strong intermolecular forces; gases have widely spaced molecules.

Concept / Approach:
In liquids, adjacent layers resist relative motion largely because of molecular cohesion forces; raising temperature weakens cohesion, typically lowering viscosity. In gases, viscosity mainly results from molecular momentum exchange during collisions; as temperature rises, collision frequency and momentum transfer increase, so gas viscosity increases.

Step-by-Step Solution:
State the claim: liquid viscosity due to cohesion.Recall temperature trends: μ_liquid decreases with T; μ_gas increases with T.These opposite trends are consistent with the different physical mechanisms.Therefore, the statement is correct for liquids.

Verification / Alternative check:
Empirical correlations (e.g., Andrade’s equation for liquids) show exponential decrease of μ with temperature; Sutherland’s law for gases shows increase, matching the mechanistic explanation.

Why Other Options Are Wrong:

• Incorrect: contradicts accepted molecular interpretation for liquids.
• “Only at high temperatures” and “only for ideal liquids” add conditions that are unnecessary and misleading.

Common Pitfalls:

• Assuming a single mechanism for both liquids and gases; their behaviors differ fundamentally.

Final Answer:
Correct