Which of the following statement is incorrect ?

Options

A. `NO` is heavier than `O_2`
B. The formula of heavy water in `D_2 O`.
C. Nitrogen diffuses faster than oxygen through an orifice.
D. `NH_3` can be used as a refrigerant.

Explanation

To determine which statement is incorrect among the given options, we will analyze each statement one by one based on the properties of the compounds mentioned.

### Step-by-Step Solution:

1. **Analyze Statement A: "NO is heavier than O2."**
- **Molecular Weight Calculation:**
- Molecular weight of NO (Nitric Oxide):
- Nitrogen (N) = 14 g/mol
- Oxygen (O) = 16 g/mol
- Total for NO = 14 + 16 = 30 g/mol
- Molecular weight of O2 (Oxygen):
- Oxygen (O) = 16 g/mol
- Total for O2 = 16 + 16 = 32 g/mol
- **Comparison:**
- Since 30 g/mol (NO) < 32 g/mol (O2), NO is lighter than O2.
- **Conclusion:**
- Statement A is **incorrect**.

2. **Analyze Statement B: "Heavy water has a formula D2O."**
- **Definition of Heavy Water:**
- Heavy water is indeed D2O, where D (deuterium) is an isotope of hydrogen with a mass number of 2.
- **Conclusion:**
- Statement B is **correct**.

3. **Analyze Statement C: "Nitrogen diffuses faster than oxygen."**
- **Graham's Law of Diffusion:**
- The rate of diffusion is inversely proportional to the square root of the molecular weight.
- **Molecular Weight Comparison:**
- Nitrogen (N2) = 28 g/mol
- Oxygen (O2) = 32 g/mol
- **Conclusion:**
- Since nitrogen has a lower molecular weight than oxygen, it will diffuse faster. Therefore, Statement C is **correct**.

4. **Analyze Statement D: "Ammonia is used as a refrigerant."**
- **Usage of Ammonia:**
- Ammonia (NH3) is widely used as a refrigerant in industrial applications.
- **Conclusion:**
- Statement D is **correct**.

### Final Conclusion:
The only incorrect statement among the options is **Statement A: "NO is heavier than O2."**

### Answer:
**Option A** is the incorrect statement.

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