The law of definite proportions is not applicable to nitrogen oxide because

Options

A. Nitrogen atomic weight is not constant
B. Nitrogen molecular weight is variable
C. Nitrogen equivalent weight is variable
D. Oxygen atomic weight is variable

Explanation

### Step-by-Step Solution:

1. **Understanding the Law of Definite Proportions**:
The law of definite proportions states that a chemical compound always contains its component elements in fixed ratio by mass, regardless of the source or how it was prepared.

2. **Identifying Nitrogen Oxides**:
Nitrogen can combine with oxygen to form several different oxides, such as:
- Nitric oxide (NO)
- Nitrogen dioxide (NO₂)
- Dinitrogen trioxide (N₂O₃)
- Dinitrogen pentoxide (N₂O₅)
- Dinitrogen tetroxide (N₂O₄)

3. **Variable Composition of Nitrogen Oxides**:
Each of these nitrogen oxides has a different ratio of nitrogen to oxygen. For example:
- NO has a 1:1 ratio of nitrogen to oxygen.
- NO₂ has a 1:2 ratio of nitrogen to oxygen.
- N₂O₅ has a 2:5 ratio of nitrogen to oxygen.

4. **Conclusion on Applicability**:
Because nitrogen can form multiple oxides with varying ratios of nitrogen to oxygen, the law of definite proportions does not apply to nitrogen oxides. Each oxide has a distinct composition, which contradicts the principle of fixed ratios in the law.

5. **Final Answer**:
The law of definite proportions is not applicable to nitrogen oxides because nitrogen can form multiple oxides with varying ratios of nitrogen to oxygen, leading to different compositions.