Which of the following pollutants is not present in the smoke emitted from the vehicles?

Options

A. Ammonia
B. Carbon monoxide
C. Lead
D. None of these

Explanation

To determine which pollutant is not present in the smoke emitted from vehicles, we can analyze the options provided:

1. **Ammonia**: This is a compound that is not typically found in the exhaust emissions from vehicles. It is not a product of combustion processes that occur in engines.

2. **Carbon monoxide**: This is a common pollutant found in vehicle emissions. It is produced during the incomplete combustion of carbon-containing fuels.

3. **Lead**: This was historically present in vehicle emissions, especially when leaded gasoline was used. Although leaded gasoline has been phased out in many countries, lead can still be found in some emissions due to other sources.

4. **None of these**: This option suggests that all the pollutants listed are present in vehicle emissions.

Now, analyzing the options:
- Carbon monoxide and lead are both present in vehicle emissions.
- Ammonia is not typically found in vehicle exhaust.

Thus, the correct answer is **A. Ammonia**.

### Step-by-Step Solution:
1. **Identify the pollutants listed**: Ammonia, carbon monoxide, lead, and none of these.
2. **Analyze each pollutant**:
- Carbon monoxide: Present in vehicle emissions.
- Lead: Historically present, but still can be found in some emissions.
- Ammonia: Not present in vehicle emissions.
3. **Determine the correct answer**: Since ammonia is not found in vehicle smoke, the answer is A.