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CGPET 2019 Solved Paper

Section: Chemistry

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Question : 57 of 150

Marks: +1, -0

The Nessler's reagent contains

$[{Hgl} 2]^{2-}$
$[{Hg}_{2}]^{2+}$
$[{Hg}]^{2+}$
$[{Hgl}_{4}]^{2-}$

Solution:

Nessler's reagent is

{K}_{2} {HgI}_{4}

. It is a basic solution of potassium mercuric iodide which gives reddish brown ppt. of millon's base

[{H}_{2} {N}-{HgO}-{HgI}]

with

{NH}_{3}

, as follows

{NH}_{3}+2 {K}_{2} {HgI}_{4}+3 {KOH} \rightarrow

{{H}_{2} {N}-{HgO}-{HgI}}↙{(lodide of millon's base) Brown ppt. }+7 {KI}+2 {H}_{2} {O}

Thus, it can give

[{HgI}_{4}]^{2-}

ions so, option

({d})

is the correct answer.

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