Question

Identify change in oxidation state of oxidising agent in following redox reaction.
\(3\text{H}_3\text{AsO}_{3(aq)}+\text{BrO}_{3(aq)}^-⟶\text{Br}_{(aq)}^-+3\text{H}_3\text{AsO}_{4(aq)}\)

• A. \(-1 \text{to} +5\)
• B. \(+5 \text{to} -1\)
• C. \(+3 \text{to} +5\)
• D. \(+5 \text{to} +3\)

Hint:

The oxidising agent is reduced; find the oxidation number of bromine before and after.

Answer 1

The Correct Option is B

Step 1: Method:
Assign oxidation numbers to each element and see which one decreases.

Step 2: Arsenic:
As changes from +3 to +5, so it loses 2 electrons per atom. That makes H$_3$AsO$_3$ the reducing agent.

Step 3: Bromine:
Bromine goes from +5 in bromate to -1 in bromide, gaining 6 electrons. This matches $3 \times 2 = 6$ electrons lost by 3 arsenic atoms, so the equation balances. The oxidising agent shifts from +5 to -1, option (B).

Final Answer:
Option (B). \[ \boxed{\text{(B) } +5 \text{ to } -1} \]