Which of the following is unstable?

Suspension

The correct answer is option 2. Suspension.

From the choices you provided, the most unstable option is Suspension.

Here is a breakdown of the stability of each mixture:

True solution: A true solution is the most stable of the three. The solute particles are extremely small (less than 1 nanometer) and evenly dispersed throughout the solvent. They are essentially invisible and won't separate or settle out of the solution over time.

Colloidal solution: Colloidal solutions have particles larger than true solutions (ranging from 1-100 nanometers) but smaller than suspensions. These particles exhibit Brownian motion, which is a constant, random movement that helps them stay suspended. However, colloidal solutions can show some degree of instability over time. If left undisturbed for a prolonged period, some larger particles might settle out due to gravity.

Suspension: Suspensions have the largest particle size (greater than 100 nanometers) among these three. The particles are not dissolved but dispersed throughout the liquid. Due to gravity, these suspended particles will eventually settle down if the mixture is left undisturbed. This makes suspensions the least stable of the three types of mixtures.

Therefore, suspensions are considered unstable because the dispersed particles tend to separate from the liquid medium over time.