Question

Sodium thiosulphate is used in photography

• A. as $AgBr$ grain is reduced to non-metallic silver
• B. to convert metallic silver into silver salt
• C. to remove reduced silver
• D. to remove undecomposed $AgBr$ in the form of $Na_3 \,[Ag(S_2O_3 )_2]$ (a complex salt)

Answer 1

Answer: (D)

In photography, used $AgBr$ is removed with the help of sodium thiosulphate, i.e., hypo.

$\underset{\text{silver bromide}}{AgBr} +\underset{\text{sodium thiosulphate}}{2 Na _{2} S _{2} O _{3}} \longrightarrow \underset{\text{sodium argento thiosulphate}}{Na _{3}\left[ Ag \left( S _{2} O _{3}\right)_{2}\right]}+ NaBr$