Question

Hypo is used in photography because:
(A) It acts as an oxidizing agent
(B) It acts as a reducing agent
(C) It acts as a catalyst
(D) It removes insoluble AgBr in the form of a soluble complex

Answer 1

Hint: Hypo solution is also called sodium thiosulphate. The photography film contains silver halide crystals that define the resolution, sensitivity, and contrast of the film. The removal of silver halide crystals is a function of the hypo solution.

Complete step by step answer:
We know that the photography film is coated with a layer of silver halide crystals. During the development of the image, this plate is exposed to a low amount of sunlight. This develops a partial image on the plate which is almost invisible which is called a latent image. As this plate contains silver halide crystals when they are exposed to sunlight, silver ion gets reduced to silver. These silver atoms form traces on the photography plate which obstruct light and appear black. Now the hypo solution is the abbreviation for sodium hypo- sulphite. The use of hypo solution is that it removes residual silver halide from the films.
The silver halide molecules that are unconverted in the exposure of light needed to form a clear image. To remove the remaining silver halide crystals sodium thiosulphate solution is used. When we wash the photographic plates in the solution silver halide molecules will be converted into a soluble complex and separate.
The reaction will be as follows
$2N{a_2}{S_2}{O_3} + AgBr \to N{a_3}[Ag{({S_2}{O_3})_2}] + NaBr$
So the hypo is used in photography because it removes insoluble AgBr in the form of a soluble complex $[Ag({S_2}{O_3})]_2^{3 - }$

So, the correct answer is Option D.

Note: Removal of silver halide crystals is called fixing of image. Here ammonia can also be used as a complex-forming agent. Hypo solutions are used in the image development process.