Question

Which of the following are colloids?
A.Milk
B.Ice cream
C.Urea solution
D.Blood

Answer 1

Hint: A colloidal solution is a mixture in which microscopically dispersed insoluble particles of one substance are suspended in the other. A colloid shows some interesting optical properties like Tyndall effect, absorption of light etc.

Complete step by step answer:
A colloid is a homogenous non-crystalline mixture consisting of large molecules as one of the substances disperses through the other substance. They include gels, emulsions, sols etc. They cannot be separated by simple filtration or centrifugation. The size of particles range from ${\text{1 nm}}$ to ${{1 \mu m}}$ .
In option A, milk is an emulsion of fat dispersed in water. It has tiny fat particles suspended in the liquid. It can be separated into butter or cream. So, milk is a colloid.
In option B, ice cream is also an emulsion of fat dispersed in liquid. It has ice crystals, fat particles dispersed in a mixture of water, sugar and air bubbles. The size of particles range from ${{20 - 50 \mu m}}$ . So, ice cream is also a colloidal solution.
In option C, urea solution contains urea dissolved in water. The solution contains urea as solute and water as solvent and both of them are in the same phase. Thus, urea solution is not a colloid.
In option D, blood is a fluid which contains red blood cells, white blood cells and platelets all dissolved in the fluid called plasma. Thus, blood is a colloid.

$\therefore $ The correct options are option A B and D.

Note:
Unlike solutions, in which solute and solvent are in the same phase, in colloids both the particles are always in different phases. The particles are always suspended or take a very long time to settle in the mixture. Colloids can be separated by peptisation or coagulation.