In which part of lungs gaseous exchange takes place in human :

Options

A. Trachea & alveolar duct
B. Trachea & bronchi
C. Alveolar duct & alveoli
D. Alveoli & Trachea

Answer

To answer the question "In which part of lungs does gaseous exchange take place in humans?", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the specific part of the lungs where the exchange of gases occurs.

2. **Identifying the Options**: We need to evaluate the provided options to determine which one correctly identifies the site of gas exchange.

3. **Evaluating Option 1 - Trachea and Alveolar Duct**:
- The trachea, also known as the windpipe, primarily functions to transport air to and from the lungs. It does not participate in gas exchange.
- The alveolar duct leads to the alveoli but does not itself facilitate gas exchange.
- **Conclusion**: This option is incorrect.

4. **Evaluating Option 2 - Trachea and Bronchii**:
- Similar to the first option, the trachea is involved in air transport.
- The bronchii (the branches of the trachea that lead into each lung) also serve as passageways for air and do not facilitate gas exchange.
- **Conclusion**: This option is also incorrect.

5. **Evaluating Option 3 - Alveolar Duct and Alveoli**:
- The alveoli are tiny air sacs located at the end of the respiratory tree and are the primary sites for gas exchange.
- The alveolar ducts lead to the alveoli and are part of the structure that allows for this exchange.
- **Conclusion**: This option is correct as gas exchange occurs in the alveoli.

6. **Evaluating Option 4 - Alveoli and Trachea**:
- While the alveoli are indeed where gas exchange occurs, the trachea does not participate in this process as it is only a passageway for air.
- **Conclusion**: This option is incorrect.

### Final Answer:
The correct answer is **Option 3: Alveolar Duct and Alveoli**, as this is where the gaseous exchange takes place in the human lungs.

---