Once black and white photographic film has been developed, any unreacted silver bromide is eliminated by treatment with sodium thiosulfate. $\text{AgBr} + 2\text{Na}_2\text{S}_2\text{O}_3 \rightarrow 4\text{Na}^+ + \text{Br}^- + [\text{Ag(S}_2\text{O}_3)_2]^{3-}$ What role does the thiosulfate ion play?
- Ato make the silver ions soluble
- Bto oxidise the silver ions
- Cto reduce the bromine
- Dto reduce the silver ions