What is the minimum temperature of fixer solution?

• A. 20°C
• B. 21°C
• C. 15°C
• D. 25°C

Answer: (B)

Fixer temperature determines how quickly and how completely the fixer can dissolve unexposed silver halide. The reaction rate of the fixer and the diffusion of chemicals into the emulsion speed up with warmth, so if the fixer is too cool, fixing becomes slow and incomplete, leading to residual silver and inconsistent results. In practice, about 21°C is used as the minimum to ensure reliable fixing without going too warm for routine processing. This keeps processing times predictable and avoids the drawbacks of under-fixation. Temperatures much lower (like 15°C) slow the process too much, while higher temperatures (around 25°C) are acceptable but not the minimum.