What does the fixer do in the x-ray processing cycle?

The fixer plays a crucial role in the x-ray processing cycle by removing unexposed silver halide crystals from the photographic film. During the development stage, the film is exposed to light and dark areas form based on the exposure. After development, the remaining unexposed silver halide crystals, which appear as clear areas, need to be eliminated to prevent further chemical reaction that would lead to fogging or degradation of the image. The fixer does this by chemically converting the unexposed crystals into a soluble form that can then be washed away, thereby stabilizing the image and ensuring that only the developed areas remain visible.

The other functions mentioned in the choices do not accurately describe the principal action of the fixer. For instance, enhancing image contrast is primarily the role of the developer, while converting silver to a metallic form occurs during the development rather than fixation. Strengthening the film emulsion is not a function of the fixer; rather, it involves the composition of the film itself.