State the importance of coordination compounds in photography.

(N/A) In black and white photography,the developed film is fixed by washing it with a hypo solution (sodium thiosulphate). The hypo solution dissolves the undecomposed $AgBr$ to form a soluble complex ion,$[Ag(S_2O_3)_2]^{3-}$,which can be washed away. The reaction is: $AgBr(s) + 2Na_2S_2O_3(aq) \rightarrow Na_3[Ag(S_2O_3)_2](aq) + NaBr(aq)$.