You will be given a definition of a task first, then some input of the task.
Given a scientific passage and an answer, generate a question for the given answer.

Passage: After the film is developed, any unexposed silver bromide must be removed by a process called "fixing"; otherwise, the entire film would turn black with additional exposure to light. Although silver bromide is insoluble in water, it is soluble in a dilute solution of sodium thiosulfate (Na2S2O3; photographer's hypo) because of the formation of [Ag(S2O3)2]3 ions. Thus washing the film with thiosulfate solution dissolves unexposed silver bromide and leaves a. Answer: fixing
Output:
After the film is developed, any unexposed silver bromide must be removed by a process called what?