In the chemical change `aN_(2)H_(4)+bBrO_(3)^(-)toaN_(2)+bBr^(-)+6H_(2)O`, answer the following questions:
The element oxidised and reduced in the reaction are respectively:

Options

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

Answer

To determine the elements oxidized and reduced in the reaction \( aN_2H_4 + bBrO_3^- \rightarrow aN_2 + bBr^- + 6H_2O \), we need to analyze the oxidation states of the elements involved in the reaction.

### 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:**
- For \( N_2H_4 \):
- The oxidation state of nitrogen in \( N_2H_4 \) can be calculated. Each hydrogen has an oxidation state of +1. Thus, for two nitrogen atoms:
\[ 2x + 4(+1) = 0 \quad \Rightarrow \quad 2x + 4 = 0 \quad \Rightarrow \quad 2x = -4 \quad \Rightarrow \quad x = -2 \]
Therefore, the oxidation state of nitrogen in \( N_2H_4 \) is -2.

- For \( N_2 \):
- In elemental nitrogen (\( N_2 \)), the oxidation state is 0.

- For \( BrO_3^- \):
- The oxidation state of bromine can be calculated as follows. Let the oxidation state of Br be \( y \):
\[ y + 3(-2) = -1 \quad \Rightarrow \quad y - 6 = -1 \quad \Rightarrow \quad y = +5 \]
Therefore, the oxidation state of bromine in \( BrO_3^- \) is +5.

- For \( Br^- \):
- The oxidation state of bromine in \( Br^- \) is -1.

3. **Identify Oxidation and Reduction:**
- **Oxidation:** An increase in oxidation state. Here, nitrogen changes from -2 in \( N_2H_4 \) to 0 in \( N_2 \). This is an increase in oxidation state, indicating that \( N_2H_4 \) is oxidized.
- **Reduction:** A decrease in oxidation state. Here, bromine changes from +5 in \( BrO_3^- \) to -1 in \( Br^- \). This is a decrease in oxidation state, indicating that \( BrO_3^- \) is reduced.

4. **Conclusion:**
- The element oxidized in the reaction is \( N_2H_4 \) (hydrazine).
- The element reduced in the reaction is \( BrO_3^- \) (bromate ion).

### Final Answer:
The element oxidized and reduced in the reaction are respectively: \( N_2H_4 \) and \( BrO_3^- \).

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