In black and white photography, the developed film is fixed by washing with

Explanation

Developer is usually a weak reducing agent like potassium ferrous oxalate, an alkaline solution of pyrogallol or an alkaline solution quinol. In the process of development of the photographic film, the exposed/activated AgBr grains are preferentially reduced by one of the reducing agent described above.

The photographic film is then fixed by washing with hypo solution to remove the unreduced AgBr grains from the film. ltBrgt `AgBr+2Na_(2)S_(2)O_(3)toNa_(3)[Ag(S_(2)O_(3))_(2)]+NaBr`.
`S_(2)O_(3)^(2-)+H_(2)Oto2SO_(2)+2H^(+)+4e^(-)`
`S_(2)O_(3)^(2-)+6H^(+)to2S darr("white milky")+3H_(2)O`.