Classification – Odd one out (measurement units: mass vs volume): Choose the unit that is not a unit of mass: Gallon, Ton, Quintal, Kilogram.

Introduction / Context:
Reasoning items about units require identifying the physical quantity measured. Three options are units of mass; one measures volume, making it the unique outlier.

Given Data / Assumptions:

• Ton → mass (1000 kg in metric ton).
• Quintal → mass (100 kg).
• Kilogram → SI base unit of mass.
• Gallon → volume (U.S./Imperial liquid measure).

Concept / Approach:
Tag each unit by physical dimension: mass vs volume. Select the unit that does not measure mass.

Step-by-Step Solution:
Ton, Quintal, Kilogram → mass.Gallon → volume.

Verification / Alternative check:
Even when converting between mass and volume using density, the unit’s inherent dimension remains distinct. Gallon stays a unit of volume.

Why Other Options Are Wrong:

• Ton, Quintal, and Kilogram measure mass and thus belong to the same category.

Common Pitfalls:
Mistaking “quintal/ton” for volume due to bulk trading contexts; they are still mass units.

Final Answer:
Gallon