A researcher added certain amount of $\mathrm{HgCl}_{2}$ to water at $\mathrm{pH} 10$. He calculated the expected concentration of mercury in the water. He asked his student to measure the concentration. His student used an instrument that can measure only the free metal, $\mathrm{Hg}^{2+}$. The student observed that the concentration measured by him was significantly less than the concentration calculated by the researcher. How can he explain the paradox to the researcher?
Explanation $1$: Significant fraction of the mercury would have changed phase from aqueous to gaseous phase, thus leaving less mercury in the water.
Explanation $2$: Fraction of the mercury added to water would have formed aqueous complexes.
Explanation $3$: Fraction of the mercury added to water could have precipitated.
Choose the correct option from the following:
- only Explanation $1$ is correct
- Explanations $1$ and $2$ are correct
- Explanations $1$ and $3$ are correct
- Explanations $2$ and $3$ are correct
