What is the main ingredient in x-ray fixer responsible for removing unexposed silver halide?

The main ingredient in x-ray fixer responsible for removing unexposed silver halide is sodium thiosulfate. In the context of radiography, the role of the fixer is to stabilize the image by dissolving any unexposed silver halide crystals that remain on the film after the development process. Sodium thiosulfate acts as a highly effective fixing agent, ensuring that only the developed silver, which forms the visible image, stays on the film while the unexposed silver halide is cleared away.

This process is essential for achieving a clear and permanent radiographic image, as it prevents fogging and unwanted image development that can occur if unexposed silver halides are left on the film. Other compounds listed, such as sodium bicarbonate, calcium carbonate, and potassium chloride, do not serve this specific function in the x-ray fixing process. Sodium bicarbonate is often used as a buffer in developer solutions, while calcium carbonate and potassium chloride serve different roles that do not involve the removal of unexposed silver halide.