Write the application of coordination compounds in black and white photography.

(N/A) In black and white photography,the developed film is fixed by washing it with a solution of sodium thiosulphate $(Na_2S_2O_3)$.
This process involves the formation of a soluble coordination complex between the unreacted silver bromide $(AgBr)$ and the thiosulphate ions $(S_2O_3^{2-})$.
The chemical reaction is: $AgBr(s) + 2Na_2S_2O_3(aq) \rightarrow Na_3[Ag(S_2O_3)_2](aq) + NaBr(aq)$.
The complex formed,sodium dithiosulphatoargentate$(I)$,is water-soluble and is washed away,leaving behind the metallic silver image.