Identify the correct statement for the following.

Options

A. Tracheo-bronchial junction is at the level of fifth cervical vertebra.
B. Inspiratory capacity is the maximum volume of air that can be inspired after normal expiration
C. `pCO_2` in de-oxygenated blood is 40 mm Hg.
D. Respiratory surface area for exchange of gases is increased in emphysema

Answer

To solve the question, we need to evaluate each of the given statements and identify which one is correct. Let's analyze each option step by step.

### Step-by-Step Solution:

1. **Evaluate the First Statement:**
- The statement claims that the tracheobronchial junction is at the level of the fifth cervical vertebra.
- **Analysis:** The tracheobronchial junction is actually located between the third cervical vertebra (C3) and the seventh cervical vertebra (C7). Therefore, this statement is **incorrect**.

2. **Evaluate the Second Statement:**
- The statement mentions that the maximum volume of air that can be inspired after normal expiration is being described.
- **Analysis:** This description corresponds to the concept of "inspiratory capacity," which is indeed defined as the maximum volume of air that can be inhaled after a normal expiration. Thus, this statement is **correct**.

3. **Evaluate the Third Statement:**
- The statement asserts that the partial pressure of carbon dioxide in oxygenated blood is 40 mmHg.
- **Analysis:** In reality, the partial pressure of carbon dioxide in oxygenated blood is approximately 45 mmHg, while the partial pressure of oxygen is around 40 mmHg. Therefore, this statement is **incorrect**.

4. **Evaluate the Fourth Statement:**
- The statement claims that the respiratory surface area for gas exchange is increased in emphysema.
- **Analysis:** In emphysema, the respiratory surface area is actually decreased due to the destruction of alveoli, which leads to shortness of breath. Therefore, this statement is **incorrect**.

### Conclusion:
After evaluating all the statements, we find that the **second statement** is the only correct one: "The maximum volume of air that can be inspired after the normal expiration."

### Final Answer:
The correct statement is: **The maximum volume of air that can be inspired after the normal expiration.**

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