Question

Sodium thiosulphate, $N{a}_2{S}_2{O}_3.5H_{2}O$ is used in photography to:

• A. reduce the silver bromide grains to metallic silver
• B. convert the metallic silver to silver salt
• C. remove undecomposed AgBr as soluble silver thiosulphate complex
• D. remove reduced silver

Answer 1

Answer: (C)

${\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3+\underset{\text{ unexposed }}{\mathrm{AgBr}}\to {\mathrm{Na}}_3\mathrm{Ag}{\left({\mathrm{S}}_2{\mathrm{O}}_3\right)}_2+\mathrm{NaBr}$

The property is used for fixing in photography.