Which processing error can cause films to turn yellow-brown and emit a sulfur smell?

The correct answer is the processing error related to cold wash water. When films are processed, the temperature of the wash water is crucial for effectively removing the developer chemicals from the film after development. If the wash water is too cold, it may not adequately remove residual developer. This insufficient washing can lead to the formation of yellow-brown stains on the film due to the oxidation of the developer that remains in contact with the film surface. Additionally, such conditions can promote the development of a sulfur smell from the chemical responses occurring as the developer oxidizes and decomposes.

This highlights the importance of maintaining an appropriate wash temperature to ensure the complete removal of processing chemicals, which is vital for achieving clear and stable radiographic images.