Question

A red solid is insoluble in water. however, it becomes soluble if some $KI$ is added to water. Heating the red solid in a test tube results in liberation of some violet colored fumes and droplets of a metal appear on the cooler parts of the test tube. The red solid is

• A. $Hg{I}_2$
• B. $HgO$
• C. ${Pb}_3{O}_4$
• D. ${\left({NH}_4\right)}_2{Cr}_2{O}_7$

Answer 1

Answer: (A)

$Hg{I}_2$

$Hg{I}_2$ is orange-red in appearance and hardly soluble in water. It dissolves in excess of $I^{-}$ giving complexes $Hg{I}_3^{-}$ and $Hg{I}_4^{2-}$. Violet fumes are liberated due to the release of Iodine gas upon heating.