The aqueous solution of an unknown sodium salt gives the following reactions:
(I) It gives white turbidity with dilute $H C l$ solution.
(II) It decolourises a solution of iodine in potassium iodide.
(III) It gives a white precipitate with $A g N O_{3}$ solution which changes colours and finally becomes black on standing.
The unknown sodium salt is:

Sodium sulphite

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Sodium sulphide

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Sodium bisulphite

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Sodium thiosulphate

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Solution

The correct option is D Sodium thiosulphate
The unknown sodium salt is sodium thiosulphate $N a_{2} S_{2} O_{3}$
It gives white turbidity with dilute $H C l$ solution.
$(i) N a_{2} S_{2} O_{3} + 2 H C l \to 2 N a C l + S O_{2} + H_{2} O + S$
It decolourises a solution of iodine in potassium iodide.
$(i i) K I_{3} + 2 N a_{2} S_{2} O_{3} \to K I + 2 N a I + N a_{2} S_{4} O_{6}$
It gives a white precipitate with $A g N O_{3}$ solution which changes colours and finally becomes black on standing.
$(i i i) 2 A g N O_{3} + N a_{2} S_{2} O_{3} \to A g_{2} S_{2} O_{3} w h i t e + 2 N a N O_{3}$
$A g_{2} S_{2} O_{3} w h i t e H_{2} O - - \to A g_{2} S b l a c k + H_{2} S O_{4}$

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Similar questions

Q. The aqueous solution of an unknown sodium salt gives the following reactions.
I. It decolorises a solution of iodine in potassium iodide.
II. It gives white turbidity with

d i l . H C l

solution.
III. It gives a white precipitate with

A g N O_{3}

solution which changes colours and finally becomes black no standing.
The unknown sodium salt is :

Q. An unknown inorganic compound

(X)

loses its water of crystallisation. On heating its aqueous solution gives the following reacion:
(i) it gives a white turbidity with dilute

H C l

solution.
(ii) it decolourises a solution of iodine in

K I

.
(iii) it gives a white precipitate with

A g N O_{3}

solution which turns black on standing.
Identify compound

(X)

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