A person breathing normally at rest, takes in and expels approximately half a litre of air during each respiratory cucle. This is called

Options

A. inspiratory reserve volume
B. tidal volume
C. expiratory reserve volume
D. vital capacity.

Explanation

To solve the question, we need to identify the term that describes the volume of air a person breathes in and out during a normal respiratory cycle. Here’s the step-by-step solution:

### Step 1: Understand the Question
The question states that a person at rest takes in and expels approximately half a liter of air during each respiratory cycle. We need to find the correct term for this volume of air.

### Step 2: Identify the Options
The options provided are:
1. Inspiratory reserve volume
2. Tidal volume
3. Expiratory reserve volume
4. Vital capacity

### Step 3: Analyze Each Option
- **Inspiratory Reserve Volume**: This is the additional volume of air that can be inhaled after a normal inhalation. It is much larger, typically around 2500 to 3000 ml. This option is incorrect.

- **Tidal Volume**: This is the volume of air that is inhaled or exhaled during a normal respiratory cycle. It is approximately 500 ml, which matches the description in the question. This option is correct.

- **Expiratory Reserve Volume**: This is the additional volume of air that can be exhaled after a normal exhalation. This is also not the volume of air exchanged in a normal cycle, making this option incorrect.

- **Vital Capacity**: This is the maximum amount of air a person can exhale after a maximum inhalation. It is the sum of tidal volume, inspiratory reserve volume, and expiratory reserve volume. This is not the correct answer for the question.

### Step 4: Conclusion
The correct term for the volume of air that a person breathes in and out during a normal respiratory cycle is **Tidal Volume**.

### Final Answer
**Tidal Volume**

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