Which of these statement is true for sodium thiosulphate ?

Options

A. it acts as an antichlor
B. it is used as an reducing agent in iodometric titration.
C. it reacts with hydrochloric acid to form `SO_(2)` and sulphur
D. it is used in photography as hypo to dissolves exess of AgBr as soluble complex.

Answer

ABCD

Explanation

(A) It removes the chorine from the surface of fibres (while deying) according to following reaction.
`Na_(2)S_(2)O+4Cl_(2)+5H_(2)O to 2NaHSO_(4)+8HCl`
Therefore, it is known as antichlor.
(B)`I_(3)^(-)+S_(2)O_(3)^(2-) to 3I^(-)+S_(4)O_(6)^(2-)`
(C ) `S_(2)O_(3)^(2-)+H^(+) to S darr ("white") +SO_(2)+SO_(2)+H_(2)O` ("disproportionation reaction").
`(D)2S_(2)O_(3)^(2-)+Ag^(+) to [Ag(S_(2)O_(3))_(2)]^(3-)` ("soluble complex") or `[Ag(S_(2)O_(3))_(3)]^(5-)`
This reaction is utlized in photography where hypo is used as fixer.