`NO_(x)` contributes to all, except

Options

A. Secondary pollutant formation
B. Acid rains
C. Pheophytization
D. Photochemical smog

Answer

To solve the question "NO_(x) contributes to all, except", we need to analyze the options provided and determine which one does not involve the contribution of NO_(x).

### Step-by-Step Solution:

1. **Understanding NO_(x)**:
- NO_(x) refers to nitrogen oxides, which include NO (nitric oxide) and NO₂ (nitrogen dioxide). These compounds play significant roles in atmospheric chemistry and pollution.

2. **Analyzing the Options**:
- **Option 1: Secondary Pollutant Formation**:
- NO_(x) contributes to the formation of secondary pollutants. For instance, it reacts with volatile organic compounds (VOCs) to form peroxyacetyl nitrate (PAN), which is a secondary pollutant.
- **Conclusion**: NO_(x) does contribute to secondary pollutant formation.

- **Option 2: Acid Rain**:
- NO_(x) is involved in the formation of acid rain. When NO_(x) reacts with water, it produces nitric acid (HNO₃), which contributes to acid rain.
- **Conclusion**: NO_(x) does contribute to acid rain formation.

- **Option 3: Pheophytization**:
- Pheophytization is a process related to the degradation of chlorophyll, leading to the formation of pheophytin, which is a pigment that does not participate in photosynthesis. This process is not directly influenced by NO_(x).
- **Conclusion**: NO_(x) does not contribute to pheophytization.

- **Option 4: Photochemical Smoke**:
- Photochemical smoke, which includes pollutants like ozone (O₃) and PAN, is formed through reactions involving NO_(x) and VOCs. Therefore, NO_(x) contributes to photochemical smoke formation.
- **Conclusion**: NO_(x) does contribute to photochemical smoke.

3. **Final Answer**:
- Based on the analysis, the option that NO_(x) does not contribute to is **Option 3: Pheophytization**.

### Summary:
The correct answer to the question "NO_(x) contributes to all, except" is **Pheophytization**.