When a person breathes out normally, then the amount of air which remains in the lung after a normal expiration is

Options

A. expiratory reserve volume.
B. expiratory capacity.
C. Functional residual capacity (FRC).
D. residual volume .

Answer

To solve the question regarding the amount of air that remains in the lungs after a normal expiration, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks for the amount of air that remains in the lungs after a normal expiration. This is a key concept in respiratory physiology.

2. **Define Key Terms**:
- **Residual Volume (RV)**: This is the volume of air that remains in the lungs after a person has exhaled as much air as possible. It prevents the lungs from collapsing and is typically around 1100 to 1200 ml.
- **Expiratory Reserve Volume (ERV)**: This is the additional amount of air that can be forcibly exhaled after the expiration of a normal tidal volume. It is also approximately 1100 ml.

3. **Identify Relevant Volumes**:
- After a normal expiration, the air that remains in the lungs consists of both the residual volume and any air that was not exhaled during normal breathing (which can be considered part of the functional residual capacity).

4. **Calculate Functional Residual Capacity (FRC)**:
- The Functional Residual Capacity (FRC) is the total amount of air remaining in the lungs after a normal expiration and is the sum of Residual Volume (RV) and Expiratory Reserve Volume (ERV).
- FRC = RV + ERV
- Given that RV is approximately 1100 to 1200 ml and ERV is approximately 1100 ml, the FRC can be estimated.

5. **Select the Correct Answer**:
- The question specifically asks for the amount of air remaining after normal expiration, which is essentially the FRC.
- Therefore, the correct answer is that the amount of air remaining in the lungs after a normal expiration is the Functional Residual Capacity (FRC).

### Final Answer:
The amount of air that remains in the lung after a normal expiration is approximately 2200 to 2300 ml (sum of RV and ERV).