What kind of reagent is used as developer in photography?

In Photography, a common developer reagent is a solution containing hydroquinone or metol, often combined with other chemicals like sodium sulfite and p-aminophenol. These developers reduce exposed silver halides in photographic film or paper to form a visible image. The choice of developer can affect the contrast, grain, and overall tonal range of the photograph. Developers can be used in various forms, including liquid, powder, or tablet.