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Question

Which of the following is NOT an example of a colloidal solution?

This question was previously asked in
RRB Group D 2024 Question Paper PDF (27-Dec-2025) (Shift 2)
The correct answer is

Air

A colloidal solution (colloid) has dispersed particles ranging from 1 nm to 1000 nm that are suspended in a dispersion medium. Smoke is a colloid (solid particles in gas), Milk is a colloid (fat globules in water — an emulsion), and Mist is a colloid (liquid droplets in gas — an aerosol).

Air, in its pure form, is a homogeneous mixture of gases (nitrogen, oxygen, argon, CO₂, etc.). All components are molecular in size (well below 1 nm), so they form a true solution, not a colloid. There is no separate dispersed phase of colloidal particle size.

Hence, Air is NOT an example of a colloidal solution.

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