The Lassiagne's extract is boiled with dil HNO _ 3 before testing...

The Lassiagne's extract is boiled with dil

{HNO}_{3}

before testing for halogens because,

Options

A $AgCN$ is soluble in ${HNO}_{3}$
BSilver halides are soluble in ${HNO}_{3}$
C ${Ag}_{2}S$ is soluble in ${HNO}_{3}$
D ${Na}_{2}S$ and $NaCN$ are decomposed by ${HNO}_{3}$

Correct answer

D. ${Na}_{2}S$ and $NaCN$ are decomposed by ${HNO}_{3}$

Step-by-step solution

The Lassaigne’s extract is first boiled with dil. HNO₃ to decompose cyanide or sulphide of sodium (NaCN or Na₂S) formed during Lassaigne’s test. These ions would otherwise interfere with silver nitrate test for halogen.

$NaCN ( aq ) + {HNO}_{3} ( aq ) \to {NaNO}_{3} ( aq ) + HCN ( ↑ )$

${Na}_{2}S ( aq ) + 2{HNO}_{3} ( aq ) \to 2{NaNO}_{3} ( aq ) + {H}_{2}S ( ↑ )$

Hence option D is the answer.

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