An aqueous solution containing 1 mol of `HgI_(2)` and 2 mol of Nal is orange in colour .On addition od excess NaI , the solution becomes colourless .The orange colour reappears on subsequent addition of `NaOCl`.

Explanation

`HgI_(2)` is having orange / scarlet colour it dissolve in sodium iodide due to the formation of a complex .
`HgI_(2) + 2Nal rarr Na_(2)HgI_(4)`
with `NaOCI` agent a precipitate of `HgI_(2)` is formed
`3Na_(2)HgI_(4) + 2NaOCI + 2H_(2)O rarr 3HgI_(2) + 2NaI_(3) + 4NaOH + 2NaCI`