Which among the following is NOT true about a solution and the solute concerned?

The particles of the solute settle down at the bottom when the solution is kept undisturbed

The correct answer is option 3. The particles of the solute settle down at the bottom when the solution is kept undisturbed.

Let us break down the explanation for each statement:

1. The particles of the solute do not scatter a beam of light:

True: In a solution, the particles (molecules or ions) of the solute are generally very small and are uniformly distributed in the solvent. Because of this homogeneous distribution, solutions usually do not scatter light, and they do not show the Tyndall effect. The Tyndall effect is the scattering of light by colloidal particles.

2. A solution is a homogeneous mixture:

True: Solutions are indeed homogeneous mixtures. This means that at the molecular level, the solute particles are uniformly distributed throughout the solvent, resulting in a consistent composition and properties throughout the mixture.

3. The particles of the solute settle down at the bottom when the solution is kept undisturbed:

False:  This statement is not true for solutions. In solutions, the solute particles do not settle down over time. Solutions are stable mixtures where the solute particles are dispersed evenly and do not separate or settle out, making them different from suspensions or colloids where settling may occur.

4. The particles of the solute cannot be seen:

True:  In true solutions, the particles of the solute are very small and molecular or ionic in nature. They are generally not visible to the naked eye and cannot be seen even with a microscope. This is a characteristic feature of solutions.

So, the incorrect statement is the third one, as solute particles in a solution do not settle down at the bottom when the solution is left undisturbed.