Sodium thiosulphate is used in photography
B
To remove undecomposed $$AgBr$$ in the form of $$Na_3[Ag(S_2O_3)_2]$$ (a complex salt)
C
To convert metallic silver into silver salt
D
$$AgBr$$ grain is reduced to non-metallic silver
Correct option is D. To remove undecomposed $$AgBr$$ in the form of $$Na_3[Ag(S_2O_3)_2]$$ (a complex salt)
Hypo solution ($$Na_2S_2O_3$$) is used in photography to remove the unaffected $$AgBr$$ in the form of soluble complex.
$$AgBr+2Na_2S_2O_3\to \underset{\text{Sodium argentothiosulphate}}{Na_3[Ag(S_2O_3)_2]}+NaBr$$