With respect to lubricating oils, what statement is true concerning viscosity and viscosity index?

Correct Answer: Option A — Viscosity is a measure of an oil's internal resistance to flow and viscosity index is a measure of an oil's ability to resist change in viscosity as the temperature changes.

Viscosity defines an oil's resistance to flow, a critical property for film strength. The Viscosity Index (VI) quantifies the rate of viscosity change relative to temperature fluctuations. A high VI indicates the oil maintains a stable viscosity across a wider operating temperature range, which is essential for consistent machinery lubrication.