In black and white photography, the developed photographic film is chemically "fixed" by washing it — d and f Block Elements Chemistry Question

💡 Solution & Explanation

After the photographic film is exposed to light and developed (where exposed $AgBr$ is reduced to metallic $Ag$), the remaining unexposed $AgBr$ must be removed so the film does not turn completely black when brought into the light. Hypo solution ($Na_2S_2O_3$) acts as a fixing agent. It utilizes the complex-forming ability of transition metals, reacting with insoluble $AgBr$ to form the highly water-soluble coordination complex Sodium dithiosulphatoargentate(I), $Na_3[Ag(S_2O_3)_2]$, which is then safely washed away.