Give equation and describe the process for the developing of black and white photographic film. When sodium thiosulphate solution is treated with acidic solution turns milky white. Give the half reaction of the above described process.

Answer

Developer is usually a weak reducing agent like potassium ferrous oxalate, an alkaline solution of pyrogallol or an alkaline solution of quinol.
In the process of development of the photographic film, the exposed//activated `AgBr` grain are preferentially reduced by one of the reducing agent described above.
`(##RES_INO_CHM_V01_XII_V02_C01_S01_262_A01##)`
`AgBr+Ag(s)+Br^(-)`
The photographic film is then by washing with hypo solution to remove the unreduced `AgBr` grain from film.
`AgBr+2Na_(2)S_(2)O_(3) to Na_(3)[Ag(S_(2)O_(3))_(2)]+NaBr`.
`S_(2)O_(3)^(2-)+H_(2)O to 2SO_(2)+2H^(+)+4e^(-)`
`S_(2)O_(3)^(2-)+6H^(+) to 2Sdownarrow("white milky")+3H_(2)O`.