Question

The image of an exposed and developed photographic film is due to:
A.AgBr
B.${[Ag{({C_2}{O_3})_2}]^{3 + }}$
C.Ag
D.$A{g_2}O$

Answer 1

Photographic film is basically a strip of transparent plastic that is covered in or coated with a gelatine-like emulsion. This emulsion contains microscopically small silver halide crystals. These silver halide crystals are sensitive to light. The characteristic features of the crystal - like crystal size determine the sensitivity, contrast and resolution of the film.

Complete Step-by-Step Answer:
Before we move forward with the solution of the given question, let us first understand some important basic concepts.
If exposed directly to light, this emulsion would darken and the film would then become useless. To counter this issue, the exposure time of the film is so adjusted that only a very slight chemical change which is proportional to the amount of light absorbed by each crystal occurs. This results in the formation of a latent image in the emulsion. This can be later used to develop a visible image.
To explain this entire process in a gist, the film contains a layer of crystals of silver halide, which usually is silver bromide or AgBr. Another compound used to develop the image is ${K_2}Fe{({C_2}{O_4})_2}$ . The entire chemical process can be represented as:
${K_2}Fe{({C_2}{O_4})_2} + AgBr \to Ag \downarrow + KFe{({C_2}{O_4})_2} + KBr$
Here, Ag is precipitated to form the actual visible images on the developed image.
Hence, Option C is the correct option

Note: These films are sensitive to ultraviolet light, gamma rays, x – rays and high energy particles as well. The silver halide crystals which are present in the emulsion are sensitive to the blue part of the spectrum, which produces renditions of some coloured objects that may look quite unnatural. This issue was later resolved by the introduction of certain dyes that enabled the silver halide crystals to be sensitive to the other colours of the spectrum as well. Such films are known as panchromatic films.