What is the primary function of sodium thiosulfate in the developing process?

Sodium thiosulfate plays a crucial role in the developing process by serving as a fixing agent that removes unexposed silver halide crystals from the film. After the film has been exposed to radiation and processed in the developer, sodium thiosulfate is utilized in the fixer solution to ensure that only the areas of the film that have been exposed to X-rays remain opaque. This helps in rendering the radiograph permanent and stable for viewing.

By effectively clearing away the unexposed silver halide crystals, sodium thiosulfate prevents further unwanted darkening of the image and enhances the overall quality of the radiograph. This step is critical in achieving a clear, diagnostic-quality image that is free from any artifacts caused by undeveloped silver halide.

The other options may describe processes that occur during film processing but do not accurately capture the primary action of sodium thiosulfate, which is focused on the removal of unexposed crystals.