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 point as it specifies "normal expiration."

2. **Identify the Relevant Terms**:
- **Expiratory Reserve Volume (ERV)**: This is the additional volume of air that can be forcibly exhaled after a normal expiration. This does not apply here since we are discussing normal expiration.
- **Expiratory Capacity**: This refers to the total volume of air that can be expired after a normal inspiration. This is also not applicable since it does not specifically address the air remaining after a normal expiration.
- **Functional Residual Capacity (FRC)**: This is the volume of air remaining in the lungs after a normal expiration. This is likely the correct answer as it directly relates to the question.
- **Residual Volume (RV)**: This is the volume of air remaining in the lungs after a forcible expiration. This is not relevant to the question since it deals with forcible expiration.

3. **Analyze the Options**: Based on the definitions:
- ERV is not correct because it pertains to additional air that can be exhaled.
- Expiratory Capacity is not correct as it refers to total air expired after inspiration.
- Functional Residual Capacity is correct because it represents the air left in the lungs after normal expiration.
- Residual Volume is incorrect in this context as it deals with air remaining after forcible expiration.

4. **Conclusion**: The correct answer to the question is **Functional Residual Capacity (FRC)**, as it specifically refers to the volume of air remaining in the lungs after a normal expiration.

### Final Answer:
The amount of air which remains in the lung after a normal expiration is **Functional Residual Capacity (FRC)**.