An aqueous solution containing 1 mol of `HgI_(2)` and `2mol` of Nal is orange in colour. On addition of excess NaI the solution becomes colourless The orange colour reappears on subsequent addition of Na `OCI` Explain with equations .

Explanation

`HI_(2)` has orange/scarlet colour
It issolves in sodium iodide due to the formation of complex
`HgI_(2) + 2NaI rarr Na_(2) HgI_(4)`
With `NaOCI` again a precipitate of `HgI_(2)` is formed
`3Na_(2)HgI_(4) +2NaOCI+2H_(2)O`
`rarr 3HgI_(2) +2NAI_(3) + 4NaOH + 2NaCI` .