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Which of the following is used in photography?

Correct answer: B. Na2S2O3

  • A. NaHSO3
  • B. Na2S2O3
  • C. Na2S
  • D. Na2SO3

Explanation

Sodium thiosulfate, Na2S2O3, is used as photographic fixer because it dissolves unexposed silver halide by forming a soluble silver-thiosulfate complex. The likely distractor is Na2SO3, a sulfite salt with a similar formula, but sulfite does not perform the standard fixing reaction.

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