When only a little quantity of ${\mathrm{HgCl}}_2\left(s\right)$ is added to excess $\mathrm{KI}\left(aq\right)$ to obtain a clear solution, which of the following is true for this solution? (no volume change on mixing)

$\underset{b}{4\mathrm{KI}}+\underset{a}{{\mathrm{HgCl}}_2}⟶{\mathrm{K}}_2\left[{\mathrm{HgI}}_4\right]+2\mathrm{KCl}$

$$\begin{gathered} b-4a\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{-}\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{ }a\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{ }\mathit{2}a \\ \begin{array}{cccc}[2b-8a& + & 3a\mathit{ }\mathit{ }\mathit{ }+ 4a]=2b-a& \end{array} \end{gathered}$$

When volume is not changed on mixing,  the boiling point of it is lowered for this case.