Which one of the following is not a colloid?

This question was previously asked in
UPSC CAPF Previous Year Paper 4 (Held on: 26 June 2016)
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  1. Milk
  2. Mud
  3. Butter
  4. Boric acid

Answer (Detailed Solution Below)

Option 4 : Boric acid
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Detailed Solution

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The correct answer is Boric acid.

  • A colloidal solution is a solution in which microscopically dispersed insoluble particles of one substance are suspended in another substance.
  • The suspended particle in a colloid can range from 1 to 1000 nanometres in its size.
  • John Tyndall, an Irish physicist, discovered the Tyndall effect. 
  • Tyndall effect: It is the effect of scattering of light in colloidal dispersion but shows no light in a true solution. The light collides with the colloidal particles and is deviated (scattered) from its normal trajectory which is a straight line.
  • This effect is primarily used to determine whether a certain mixture is a true solution or a colloid.

Key Points

Examples of Colloids:

Dispersion Medium Dispersion Phase Type of Colloids Example
Solid Solid Solid sol Ruby Glass
Solid Liquid Solid emulsion/gel Pearl, Cheese, Butter
Solid Gas Solid foam Lava
Liquid Solid Sol Paint, Mud
Liquid Liquid Emulsion Milk
Liquid Gas Foam Whipped cream
Gas Solid Aerosol Smoke
Gas Liquid Aerosol Fog, Mist
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