Which of the following silver halides is used in photography chiefly for the production of colloidal emulsion plates ?

Options

A. AgI
B. AgBr
C. AgCI
D. AgF

Answer

A

Explanation

Silver chloried is used in photography chiefly for printing paper for lantern slides, the bromide is used in large quantities for the production of photographic films and plates (light-sensitive materials) and the iodide chiefly for the production of colloidal emulsion plates in photography. A photography plate or film is essentially a layer of an emulsion of a silver halide (most frequntly AgBr) in gelation and water applied to a glass or celluloid sheet. The AgBr with a little iodide is precipitated and the warm mixture is allowed to stand for some time. Teh process is called ripening and making the emulsion more sensitive to light. The emulsion is allowed to cool and set and then washed with water to removed soluble material. It is then melted and applied to glass or celluloid sheet and dried. After the plate or film is ready for use, the following process are undertaken for photography in stages:
(1) Exposure: Teh exposure of photographic plate or film to the object results in the photochemical decomposition of Ag halides coated on the film:
`Ag^(+) + e^(-) rarr Ag`
Consequently submicroscopic particles of Ag are formed whilst the halogen combines with the gelatin (A complex protein formed by the hydrolysis of collagen in animal cartillages and bones, by boiling with water. Soluble in water, the solution has the property of setting to a jelly).
(2) Developing: The film is now developed by adding an organic reducing agent when more AgBr is reduced, the rate of reduction depending upon the intensity of illumination during the exposure period. Thus, parts of the film which were most strongly illuminated become the darkest. It is this intensification of the latent image first formed that permits the use of short exposure times and causes Ag halide to occupy their unique position in photography.
(3) Fixing: The film is now washed with aqueous solution of sodium thiosulphate which removes the nuchanged Ag halide as a complex `[Ag(S_(2)O_(3))_(2)]^(3-)` . The negative is now ready and can be handled in day-light. In order to make print form the negative, light is allowed to pass through it on the Ag Br containing photographic paper which is then treated in a similar way as the negative. The negative image is thus reversed.