Question

Assertion: Bromide ion acts as a reducing agent in the reaction, $ 2Mn{O_4}^ - + B{r^ - } + {H_2}O \to 2Mn{O_2} + Br{O_3}^ - + 2O{H^ - } $
Reason: Oxidation number of bromine increases from $ - 1 $ .
1) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
2) Both Assertion and Reason are correct but Reason is not the correct explanation for
Assertion.
3) Assertion is correct but Reason is incorrect.
4) Both Assertion and Reason are incorrect.

Answer 1

Hint: An oxidizing agent is the one which itself undergoes reduction and helps its counterpart species present in the reaction to undergo oxidation. Whenever any species undergoes oxidation,it loses electrons and similarly, whenever any species undergoes reduction, it gains electrons. This can be seen from the oxidation state of that atom from the molecule in the reactant and product side of the reaction to if it is undergoing gain or loss of electron.

Complete answer:
In the given reaction, first we need to find the initial and final oxidation start of bromide ion in the reaction.
Here, on the reactant side, the bromide ion is present in $ - 1 $ oxidation state. In the product side, it is present as $ Br{O_3}^ - $ form, i.e. it can be seen it has the oxidation state of c, since the oxidation state of oxygen atom is $ - 2 $ .
Thus, we can see that the oxidation state of bromine goes from $ - 1 $ to $ + 5 $ . Hence, it is losing the electron, and thus is undergoing oxidation. Since it is undergoing oxidation, it is acting as a reducing agent.
Also, it is clear that its oxidation state increases from $ - 1 $ to $ + 5 $ .
Hence, in the given question, both assertion and reason given are correct.
Therefore, option $ (1) $ is correct.

Note:
The definition of oxidation and oxidizing agent can be a little confusing, and hence a clear idea of both the definitions must be known in order to avoid confusion. Also, general oxidation state of certain atoms should be remembered to carry out the oxidation state calculation which is the key factor to solve the question of the given type.