A solution of Na₂S₂O₃ is standardized iodometrically against 0.1262 g of KBrO₃. This process required 45 ml of the Na₂S₂O₃ solution. What is the strength of the Na₂S₂O₃? (K = 39, Br = 80)

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mol KBrO₃ = 0.1262/167 = 0.7557 mmol. Br goes from +5 to -1 (6e⁻), liberating 3 I₂ per BrO₃⁻: I₂ = 2.267 mmol. I₂ + 2S₂O₃²⁻ → 2I⁻ + S₄O₆²⁻: S₂O₃²⁻ = 4.534 mmol in 45 ml → 4.534/45 = 0.1 M, option (b).

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