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 expels 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 litre of air during each respiratory cycle. We need to identify what this volume is called.

### Step 2: Review the Options
We have several options to consider:
1. Inspiratory Reserve Volume (IRV)
2. Tidal Volume
3. Expiratory Reserve Volume (ERV)
4. Vital Capacity

### Step 3: Analyze Each Option
- **Inspiratory Reserve Volume (IRV)**: This is the extra amount of air that can be inhaled forcefully after a normal breath. Its volume is approximately 2500 ml to 3000 ml, which is much larger than half a litre.

- **Tidal Volume**: This is the volume of air that is inhaled and exhaled during normal breathing. The typical volume for tidal volume is approximately 500 ml, which matches the half a litre mentioned in the question.

- **Expiratory Reserve Volume (ERV)**: This is the extra amount of air that can be exhaled forcefully after a normal breath. Its volume is around 1000 ml to 1100 ml, which is also larger than half a litre.

- **Vital Capacity**: This is the total volume of air that can be inspired and expired, which is the sum of Tidal Volume, Inspiratory Reserve Volume, and Expiratory Reserve Volume. Its volume ranges from approximately 3400 ml to 4800 ml, which is again much larger than half a litre.

### Step 4: Conclusion
Based on the analysis, the correct answer is **Tidal Volume**, as it is the only option that corresponds to the volume of approximately half a litre (500 ml) of air taken in and expelled during normal breathing.

### Final Answer
**Tidal Volume**

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