Final answer:
Sodium thiosulfate, also known as hypo, is the cleaning agent that removes undeveloped silver halide crystals from photographic film.
Step-by-step explanation:
The cleaning agent that removes undeveloped silver halide crystals is sodium thiosulfate (Na2S2O3), also known as hypo. When unexposed silver halides react with sodium thiosulfate, they form a complex ion called Ag(S₂O3)2 ³−. This reaction helps remove the undeveloped silver halide crystals from photographic film.
For example, in black-and-white film development, sodium thiosulfate is used as a fixing agent. It reacts with the unexposed silver halides, converting them into a soluble complex that can be easily rinsed away.
Using sodium thiosulfate allows for efficient removal of the undeveloped silver halides, ensuring clearer, sharper images in black-and-white photography.