This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
[{'content': 'Function of hypo used in fixer is: \nSelect and explain. \nA. Inactivates the carryover developing agent, B. Dissolves and removes the unexposed silver halide, C. Prevents damage to gelatin, D. All of the above', 'role': 'user'}, {'content': "Answer: B \nExplanation: An aqueous solution of ammonium thiosulfate (“hypo”) dissolves the unexposed silver halide grains. It forms stable, water-soluble complexes with silver ions, which diffuse from the emulsion. Excessive fixation (hours) results in a gradual loss of film density because the grains of silver slowly dissolve in the acetic acid of the fixing solution.\nWhite and Pharoah's Oral\xa0 Radiology Principles and Interpretation 8th edition", 'role': 'assistant'}]