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Preparation of Hydrogen from Cold Water and Metals

When a substa...

Question

When a substance reacts with dil. sulphuric acid a light brown gas is evolved when a filter paper moistened with acidified starch iodide solution is brought on the month of the test, it is turned blue. The acidic radical in the salt is :

A

Sulphide

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B

Nitrate

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C

Carbonate

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D

Nitrite

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Solution

The correct option is D Nitrite

On treating solid nitrite with dil. $H_{2} S O_{4}$ , nitric oxide ( $N O$ ) gas is evolved which readly gives brown fumes of $N O_{2}$ with the oxygen of the air.
Nitrites react with potassium iodide in the presence of dilute sulphuric acid to liberate iodine. Iodine forms a blue-black complex with starch.
$2 K I + 2 H_{2} S O_{4} + 2 H N O_{2} ⟶ 2 K H S O_{4} + I_{2} + 2 N O + 2 H_{2} O$
$I_{2} + S t a r c h ⟶ B l u e - B l a c k C o m p l e x$

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B
C
D
E

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