Carcinogenic substance present in cigarette smoke

Options

A. Carbon monoxide
B. Benzopyrenes
C. Carbon dioxide
D. Caffein

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for a carcinogenic substance present in cigarette smoke. Carcinogenic substances are those that can lead to cancer.

2. **Composition of Cigarette Smoke**: Cigarette smoke is a complex mixture of thousands of chemicals. It is produced by burning tobacco and its additives.

3. **Identifying Carcinogens**: Among the thousands of chemicals in cigarette smoke, at least 70 are known to be carcinogenic. This means they have the potential to cause cancer.

4. **Examples of Chemicals in Cigarette Smoke**: Some of the chemicals found in cigarette smoke include:
- Nicotine
- Carbon monoxide
- Lead
- Arsenic
- Benzo[a]pyrene
- Ammonia
- Hydrogen cyanide

5. **Focusing on Carcinogenic Chemicals**: Out of the listed chemicals, we need to identify which one is specifically known as a carcinogen.

6. **Identifying Benzo[a]pyrene**: Benzo[a]pyrene is highlighted as a carcinogenic substance found in cigarette smoke. It is specifically noted for its cancer-causing properties.

7. **Exclusion of Other Options**: Other substances mentioned, such as carbon monoxide and caffeine, are not classified as carcinogens in the context of cigarette smoke.

8. **Conclusion**: The correct answer to the question is **benzo[a]pyrene**, as it is a recognized carcinogenic substance present in cigarette smoke.