In which of the following reactions is there a change in the oxidation number of nitrogen atom?

Options

A. `2NO_(2)rarrN_(2)O_(4)`
B. `NH_(3)+H_(2)OrarrNH_(4)^(+)+OH^(-)`
C. `N_(2)O_(5)+H_(2)Orarr2HNO_(3)`
D. None of these

Answer

To determine if there is a change in the oxidation number of nitrogen in the given reactions, we will analyze each reaction step by step.

### Step 1: Analyze the first reaction: NO2 → N2O4

1. **Identify oxidation states**:
- In NO2:
- Oxygen (O) has an oxidation state of -2.
- Let the oxidation state of nitrogen (N) be x.
- The equation becomes: x + 2(-2) = 0 → x - 4 = 0 → x = +4.
- In N2O4:
- There are 2 nitrogen atoms, so the oxidation state of nitrogen remains the same.
- The equation becomes: 2x + 4(-2) = 0 → 2x - 8 = 0 → 2x = 8 → x = +4.

2. **Conclusion**: The oxidation state of nitrogen is +4 in both NO2 and N2O4.
- **Change in oxidation number**: No change.

### Step 2: Analyze the second reaction: NH3 → NH4+

1. **Identify oxidation states**:
- In NH3:
- Hydrogen (H) has an oxidation state of +1.
- Let the oxidation state of nitrogen (N) be y.
- The equation becomes: y + 3(+1) = 0 → y + 3 = 0 → y = -3.
- In NH4+:
- The equation becomes: y + 4(+1) = +1 → y + 4 = 1 → y = -3.

2. **Conclusion**: The oxidation state of nitrogen is -3 in both NH3 and NH4+.
- **Change in oxidation number**: No change.

### Step 3: Analyze the third reaction: N2O5 → HNO3

1. **Identify oxidation states**:
- In N2O5:
- Oxygen (O) has an oxidation state of -2.
- Let the oxidation state of nitrogen (N) be z.
- The equation becomes: 2z + 5(-2) = 0 → 2z - 10 = 0 → 2z = 10 → z = +5.
- In HNO3:
- Hydrogen (H) has an oxidation state of +1, and Oxygen (O) has an oxidation state of -2.
- The equation becomes: z + 3(-2) + 1 = 0 → z - 6 + 1 = 0 → z - 5 = 0 → z = +5.

2. **Conclusion**: The oxidation state of nitrogen is +5 in both N2O5 and HNO3.
- **Change in oxidation number**: No change.

### Final Conclusion
After analyzing all the reactions, we find that there is no change in the oxidation number of nitrogen in any of the given reactions. Therefore, the answer is:

**None of these reactions show a change in the oxidation number of nitrogen.**

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