Question

In black and white photography, the developed film is fixed by washing with hypo solution which dissolves the under composed $AgBr$ to from a complex ion formed is:
(A). ${\left[ {Ag{{\left( {{S_2}{O_3}} \right)}_2}} \right]^{2 - }}$
(B). ${\left[ {Ag{{\left( {{S_2}{O_3}} \right)}_2}} \right]^{3 - }}$
(C). ${\left[ {Ag{{\left( {{S_2}{O_3}} \right)}_2}} \right]^ - }$
(D). None of these

Answer 1

Hint:When an undecomposed $AgBr$ is washed with hypo solution in photography, a complex ion of sodium argento thiosulphate is formed. Hypo solution is used for both film and photographic paper processing.

Complete step by step answer:
Hypo solution is an abbreviation used for sodium thio-sulphate or sodium hypo-sulfite. This chemical is used to fix the image on the photographic film after it is developed.
Hypo solution is referred to as fixer. The use of hypo solution is that it removes residual silver halides from the films. It is referred to as hypo from the original chemical name hyposulfite of soda.
Sodium thiosulfate is actually an inorganic compound having the chemical formula of $N{a_2}{S_2}{O_3}.x{H_2}O$ .
What happens when we fix the photographic film? By fixing the photographic film becomes insensitive to further action by light.
What if we do not fix the film? Without fixing the film, the remaining silver halide will lead to darkening and fogging of the image.
The reaction Involved in the process of fixing is:
$AgX + 2{S_2}O_3^{2 - } \to {\left[ {Ag{{\left( {{S_2}{O_3}} \right)}_2}} \right]^{3 - }} + {X^ - }$
$AgX + 3{S_2}O_3^{2 - } \to {\left[ {Ag\left( {{S_2}{O_3}} \right)} \right]^{5 - }} + {X^ - }$
We use fixers for processing all the commonly used films which includes. Black and white films or chromogenic films. Chromogenic means a colourless chemical compound that can be converted by a chemical reaction into a coloured compound.
After fixing the film, Washing is very much important to remove exhausted chemicals from the emulsion. If we do not do washing, it will deteriorate the image.
Hence, ${\left[ {Ag{{\left( {{S_2}{O_3}} \right)}_2}} \right]^{3 - }}$ ion is formed.
So, option (B) is correct.

Note:
The reaction of $AgBr$ with hypo solution is
$AgBr + 2N{a_2}S{O_3} \to N{a_3}\left[ {Ag{{\left( {{S_2}{O_3}} \right)}_2}} \right] + NaBr$
The complex ion argento thiosulphate is formed.