Question

Thiosulphate reacts differently with iodine and bromine in the reaction given below:  
$$ 2S_2O_3^{2-} + I_2 \rightarrow S_4O_6^{2-} + 2I^- $$ $$ S_2O_3^{2-} + 5Br_2 + 5H_2O \rightarrow 2SO_4^{2-} + 4Br^- + 10H^+ $$ 
Which of the following statements justifies the above dual behaviour of thiosulphate?

• A. Bromine undergoes oxidation and iodine undergoes reduction by iodine in these reactions
• B. Thiosulphate undergoes oxidation by bromine and reduction by iodine in these reactions
• C. Bromine is a stronger oxidant than iodine
• D. Bromine is a weaker oxidant than iodine

Answer 1

The Correct Option is C

In the reaction with I$_2$, the oxidation state of sulphur changes from $+2$ to $+2.5$.
In the reaction with Br$_2$, the oxidation state of sulphur changes from $+2$ to $+6$.
Thus, both I$_2$ and Br$_2$ are oxidants, but Br$_2$ is stronger as it increases the oxidation state of sulphur further.
Final Answer:
Bromine is a stronger oxidant than iodine.