When the silver salt film is developed, the development starts from _ _ _ _.

A: Silver halide is reduced to silver.

Analysis:

After exposure, the film will form a black image composed of metallic silver under the action of developer, which mainly includes developer, protective agent, promoter and inhibitor. Developer is the most important component in developer, and its function is to reduce the exposed silver halide into silver and turn the latent image into visible image, that is, development. Chemicals commonly used as developers are metol, hydroquinone and fenidone. The protective agent is a chemical agent such as sodium sulfite, which is added to prevent oxidation of the developer in the developer solution. The protective agent can also play the role of pollution prevention, particle development and stabilizing the developer. The function of accelerator is to strengthen the developer's development activities and speed up the development. These chemicals are borax, sodium carbonate and sodium hydroxide. The function of inhibitor is to prevent or reduce the development of fog, and the chemical substance is potassium desert.