Which one of the following is not a solution?

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Alloy

Milk

Air

Sugar

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Answer is Wrong!

This question was previously asked in

UPSC NDA-1 – 2022

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A solution is a homogeneous mixture of two or more substances. Among the given options, milk is a heterogeneous mixture (specifically a colloid).

An alloy is a homogeneous mixture of metals or a metal and a non-metal (e.g., brass, steel), so it is a solution (solid solution). Air is a homogeneous mixture of gases (primarily nitrogen and oxygen), so it is a solution (gaseous solution). Milk contains dispersed particles of fat and protein which are not uniformly distributed at the microscopic level, making it a heterogeneous mixture (colloid). Sugar itself is a pure substance (compound), but if dissolved in water, it forms a homogeneous mixture (sugar solution). However, given the options as listed, Milk is the only one that is definitively not a solution.

Mixtures can be homogeneous (solutions) or heterogeneous (suspensions and colloids). Solutions have uniform composition throughout. Colloids have particles dispersed uniformly, but these particles are larger than molecules and cause light scattering (Tyndall effect); they are considered heterogeneous. Suspensions have even larger particles that settle out over time.

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