Silver halide crystals, such as silver bromide AgBr , silver chloride AgCl , and silver iodide AgI , are light-sensitive compounds used in black and white photography. They have unique photochemical properties that enable them to produce an image when exposed to light.1. Light sensitivity: Silver halide crystals are sensitive to light, particularly in the blue and ultraviolet regions of the spectrum. When photons of light strike the surface of the crystals, they can cause a photochemical reaction, which leads to the reduction of silver ions Ag+ to metallic silver Ag0 atoms. This process is known as photolysis.2. Latent image formation: During photolysis, the metallic silver atoms form small clusters called latent image centers. These centers are not visible to the naked eye, but they serve as the foundation for the visible image that will be produced during the development process. The number of latent image centers formed is proportional to the intensity and duration of light exposure, which determines the image's contrast and tonal range.3. Development: After exposure, the photographic film or paper is treated with a chemical developer, which contains a reducing agent, typically an organic compound like hydroquinone or metol. The developer selectively reduces the silver ions in the latent image centers to metallic silver, forming larger, visible silver particles. The unexposed silver halide crystals remain unaffected and are later removed during the fixing process.4. Fixing: The fixing process involves treating the film or paper with a solution containing a chemical fixer, such as sodium thiosulfate or ammonium thiosulfate. The fixer dissolves the unexposed and undeveloped silver halide crystals, leaving behind only the metallic silver particles that form the visible image. This step ensures that the image is stable and will not continue to darken upon further exposure to light.5. Washing and drying: Finally, the film or paper is thoroughly washed with water to remove any residual chemicals and then dried. The result is a stable, black and white image composed of metallic silver particles, with the image's contrast and tonal range determined by the distribution and size of the silver particles.In summary, the photochemical properties of silver halide crystals, such as their light sensitivity and ability to form latent image centers, are crucial for producing black and white images in photography. The development, fixing, washing, and drying processes further refine and stabilize the image, resulting in a permanent, visible representation of the original scene.