In `black and white` photography, silver halide compounds are used to capture and develop images. These compounds are sensitive to light and react when exposed to it.

Option 1: AgF - Silver fluoride. While it is a type of silver halide compound, it is not commonly used in photography. Alert - correct answer should be option 2.

Option 2: AgBr - Silver bromide. This compound is widely used in `black and white` photography. It is sensitive to light and forms silver ions when exposed, resulting in the formation of a black and white image.

Option 3: AgCl - Silver chloride. Another type of silver halide compound, but it is not as light-sensitive as silver bromide. It is mainly used in medical imaging.

Option 4: Ag2SO4 - Silver sulfate. This compound is not used in photography. It is primarily used in chemical analysis and other industrial applications.

Therefore, the correct answer is option 2, AgBr, which is commonly used in `black and white` photography.