Question

Sodium thiosulphate, $Na_{2}S_{2}O_{3}.5H_{2}O$ 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)

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

The property is used for fixing in photography.