Question

Assertion: Colloidal solutions scatter the beam of light while true solutions do not.
Reason: The particles in colloidal solutions are bigger than those of true solutions.
A) Both Assertion and Reason are correct and Reason is the correct explanation for assertion.
B) Both Assertion and Reason are correct and Reason is not the correct explanation for assertion.
C) Assertion is correct but Reason is incorrect.
D) Assertion is incorrect and Reasons are correct.

Answer 1

Recall what we studied something called as tyndall effect. Tyndall effect is, in fact, the definitive test to show the difference between a true and a colloidal solution. Colloidal solution shows tyndall effect but true solution does not show this effect.

Complete solution:
Remember Colloidal solutions, or colloidal suspensions, are nothing but a mixture in which the substances are regularly suspended in a fluid. A colloid is a very tiny and small material that is spread out uniformly all through another substance. Colloidal systems can occur in any of the three key states of matter gas, liquid or solid. However, a colloidal solution usually refers to a liquid concoction. The primary distinguishing feature between a true solution and a colloidal solution is fundamentally the dimensions of the constituent parts.
Remember True Solution is a homogeneous mixture of two or more substances in which substance dissolved (solute) in solvent has the particle size of less than 10-9 m or 1 nm. Simple solution of sugar in water is an example of a true solution. Particles of true solution cannot be filtered through filter paper and are not visible to naked eye.
When light is passed through a true solution, the dissolved particles are too small to deflect the light. Suspensions may scatter light, but if the number of suspended particles is sufficiently large, the suspension may simply be opaque and the light scattering will not occur.
Tyndall effect works on the principle that light beams scatter due to the presence of large colloidal particles in the solution which separate the light however in a true solution the particles are not as large enough to scatter the light particles, that's why Tyndall effect is not seen in true solution.
Colloid particles are larger than water and large enough to show Tyndall effect.
Hence Both Assertion and Reason are correct and Reason is the correct explanation for assertion.

Hence,the correct option is (A).

Note: The main point to be remembered Distinguish between the true solution and colloidal solution. In a true solution the particle size of the substance dissolved in the solvent is less than 1nm. In a colloidal solution the particle size of the substance dissolved in the solvent is 1-1000nm, which is much greater than that true solution.