Which of the following has not adverse effect on human health?

Options

A. NO
B. `NO_(2)`
C. `SO_(2)`
D. CO

Answer

To determine which of the following options has not an adverse effect on human health, we will analyze each option provided:

1. **NO (Nitric Oxide)**
2. **NO2 (Nitrogen Dioxide)**
3. **SO2 (Sulfur Dioxide)**
4. **CO (Carbon Monoxide)**

### Step 1: Analyze NO (Nitric Oxide)
- Nitric oxide (NO) is a gas that can react with other substances in the atmosphere. While it can contribute to the formation of photochemical smog, it does not have direct adverse health effects on humans. Therefore, it is considered less harmful in terms of direct health impact.

### Step 2: Analyze NO2 (Nitrogen Dioxide)
- Nitrogen dioxide (NO2) is a significant air pollutant. It is known to cause respiratory diseases and can lead to irritation of the lungs. It can also contribute to the formation of nitric acid (HNO3), which can further affect health.

### Step 3: Analyze SO2 (Sulfur Dioxide)
- Sulfur dioxide (SO2) is another harmful pollutant. It can cause respiratory problems, irritation of the eyes, and allergic reactions. It is known to contribute to acid rain, which can have broader environmental impacts.

### Step 4: Analyze CO (Carbon Monoxide)
- Carbon monoxide (CO) is a colorless, odorless gas that can be very harmful. It interferes with the blood's ability to carry oxygen, leading to symptoms such as headaches, dizziness, and in severe cases, can be fatal.

### Conclusion
After analyzing all the options, we find that:
- **NO (Nitric Oxide)** does not have an adverse effect on human health, while **NO2, SO2, and CO** all have significant negative impacts on health.

Thus, the correct answer is **NO (Nitric Oxide)**.

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