In the following question, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices:

Assertion: Colloidal solutions do not show Brownian motion  .

Reason : Brownian motion is responsible for the stability of sols .

Assertion is false but the reason is true.

The correct answer is option 4. Assertion is false but the reason is true.

Let us break down the assertion and reason provided:

Assertion: Colloidal solutions do not show Brownian motion.

This statement is incorrect. Brownian motion is a phenomenon observed in colloidal solutions. It refers to the random, zigzag movement of microscopic particles suspended in a fluid (such as liquid or gas). This motion occurs due to the constant bombardment of the particles by the surrounding fluid molecules. Brownian motion is one of the defining characteristics of colloidal systems and is easily observable under a microscope.

Reason: Brownian motion is responsible for the stability of sols.

This statement is true. Brownian motion plays a critical role in maintaining the stability of colloidal sols. The continuous, random movement of colloidal particles prevents them from settling out of the dispersion medium due to gravity. As colloidal particles move randomly in all directions, they collide with solvent molecules, resulting in a net force that opposes sedimentation. This kinetic energy provided by Brownian motion helps keep the colloidal particles evenly dispersed and prevents their aggregation or precipitation.

In summary, while the assertion that colloidal solutions do not show Brownian motion is incorrect, the reason provided regarding the role of Brownian motion in stabilizing sols is accurate. Brownian motion is indeed essential for the stability of colloidal dispersions by preventing particle settling and maintaining uniform dispersion.