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 coloured fumes and droplets of a metal appear on the cooler parts of the test tube. The rod solid is:

Options

A. `HgI_(2)`
B. `HgO`
C. `Pb_(3)O_(4)`
D. `(NH_4)_2Cr_2O_7`

Answer

A

Explanation

When KI is added to mercuric iodide it disssolve in it and form complex.
`underset("insoluble")underset("red, solid")Hgl_(2) + Kl rarr underset("(soluble)")(K_(2)[Hgl_4])`
On heating `Hgl_2` decomposes as
`Hgl_2 hArr Hg + underset("(violet vapours)")(I_2)`