In which of the following reactions, no change in gaseous volume occurs when measured at similar T and P?

Options

A. Combination of `N_(2)` and `O_(2)` to give NO
B. Combination of `N_(2)` and `H_(2)` to form `NH_(3)`
C. Combustion of carbon to give `CO_(2)`
D. Combustion of carbon monoxide

Answer

To determine in which of the given reactions there is no change in gaseous volume when measured at similar temperature and pressure, we can apply Avogadro's law. Avogadro's law states that equal volumes of gases, at the same temperature and pressure, contain an equal number of molecules. Therefore, if the number of gaseous molecules before and after the reaction remains the same, there will be no change in gaseous volume.

Let's analyze each reaction step by step:

### Step 1: Analyze the first reaction
**Reaction:** Combination of nitrogen (N₂) and oxygen (O₂) to give nitric oxide (NO).

- **Reactants:** 1 molecule of N₂ + 1 molecule of O₂ = 2 molecules
- **Products:** 2 molecules of NO

**Conclusion:**
- Number of molecules before the reaction = 2
- Number of molecules after the reaction = 2
- **Change in volume:** No change (2 molecules before and after)

### Step 2: Analyze the second reaction
**Reaction:** Combination of nitrogen (N₂) and hydrogen (H₂) to form ammonia (NH₃).

- **Reactants:** 1 molecule of N₂ + 3 molecules of H₂ = 4 molecules
- **Products:** 2 molecules of NH₃

**Conclusion:**
- Number of molecules before the reaction = 4
- Number of molecules after the reaction = 2
- **Change in volume:** Yes, there is a change (4 molecules to 2 molecules)

### Step 3: Analyze the third reaction
**Reaction:** Combustion of carbon (C) to give carbon dioxide (CO₂).

- **Reactants:** 1 molecule of C + 1 molecule of O₂ = 2 molecules
- **Products:** 1 molecule of CO₂

**Conclusion:**
- Number of molecules before the reaction = 2
- Number of molecules after the reaction = 1
- **Change in volume:** Yes, there is a change (2 molecules to 1 molecule)

### Step 4: Analyze the fourth reaction
**Reaction:** Combustion of carbon monoxide (CO) to form carbon dioxide (CO₂).

- **Reactants:** 1 molecule of CO + 1 molecule of O₂ = 2 molecules
- **Products:** 1 molecule of CO₂

**Conclusion:**
- Number of molecules before the reaction = 2
- Number of molecules after the reaction = 1
- **Change in volume:** Yes, there is a change (2 molecules to 1 molecule)

### Final Conclusion:
The only reaction where there is no change in gaseous volume is the **first reaction**: Combination of nitrogen and oxygen to give nitric oxide (NO).

---