In the chemical change `aN_(2)H_(4)+bBrO_(3)^(-)toaN_(2)+bBr^(-)+6H_(2)O`, answer the following questions:
The species acting as oxidant and reductant respectively are:

Options

A. `BrO_(3)^(-),N_(2)H_(4)`
B. `N_(2)H_(4),BrO_(3)^(-)`
C. `N_(2),BrO_(3)^(-)`
D. `Br^(-),N_(2)H_(4)`

Answer

To determine the species acting as oxidant and reductant in the reaction \( aN_2H_4 + bBrO_3^{-} \rightarrow aN_2 + bBr^{-} + 6H_2O \), we need to analyze the changes in oxidation states of the elements involved.

### Step-by-Step Solution:

1. **Identify the Reactants and Products**:
The reactants are hydrazine (\( N_2H_4 \)) and bromate ion (\( BrO_3^{-} \)). The products are nitrogen gas (\( N_2 \)), bromide ion (\( Br^{-} \)), and water (\( H_2O \)).

2. **Determine the Oxidation States**:
- In \( N_2H_4 \), the oxidation state of nitrogen is \(-2\).
- In \( N_2 \) (elemental nitrogen), the oxidation state of nitrogen is \(0\).
- In \( BrO_3^{-} \), the oxidation state of bromine is \(+5\).
- In \( Br^{-} \), the oxidation state of bromine is \(-1\).

3. **Analyze the Changes in Oxidation States**:
- For nitrogen: The oxidation state changes from \(-2\) in \( N_2H_4 \) to \(0\) in \( N_2\). This is an increase in oxidation state, indicating oxidation.
- For bromine: The oxidation state changes from \(+5\) in \( BrO_3^{-} \) to \(-1\) in \( Br^{-}\). This is a decrease in oxidation state, indicating reduction.

4. **Identify the Oxidant and Reductant**:
- The species that gets oxidized (increases in oxidation state) is the reductant. Here, \( N_2H_4 \) is oxidized, so it acts as the reductant.
- The species that gets reduced (decreases in oxidation state) is the oxidant. Here, \( BrO_3^{-} \) is reduced, so it acts as the oxidant.

5. **Conclusion**:
- The oxidant is \( BrO_3^{-} \).
- The reductant is \( N_2H_4 \).

### Final Answer:
The species acting as oxidant and reductant respectively are:
- Oxidant: \( BrO_3^{-} \)
- Reductant: \( N_2H_4 \)

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