Addition of iodine to `KI` solution does not bring down its freezing point. But, addition of mercuric iodide to `KI` solution increases its freezing point. Give reasons.

Explanation

Addition of `I_(2)` and `HgI_(2)` separately of `KI` solution can be represented by the following equations:

From the above equations we can see that when `I_(2)` is added to `KI` solution, there is no change in the number of ions. Hence the freezing point of the solution remains unaltered. However when `HgI_(2)` is added to `KI` solution, the number of ions decreases, which raises the freezing point of the solution.