The alveolar ventilation is the

Options

A. (a) amount of air available for gas exchange in the lungs
B. (b) vital capacity divided by the respiratory rate
C. (c) tidal volume times the respiratory rate
D. (d) minute ventilation plus the dead space

Answer

### Step-by-Step Solution:

1. **Understanding Alveolar Ventilation**:
- Alveolar ventilation refers to the amount of air that reaches the alveoli and is available for gas exchange. It is crucial for maintaining adequate oxygen levels in the blood and removing carbon dioxide.

2. **Identifying the Role of Alveoli**:
- Alveoli are tiny air sacs in the lungs where the exchange of gases (oxygen and carbon dioxide) occurs. They are surrounded by capillaries that facilitate the transfer of gases between the air and the bloodstream.

3. **Evaluating the Options**:
- **Option A**: "Amount of air available for gas exchange in the lungs."
- This definition accurately describes alveolar ventilation.
- **Option B**: "Vital capacity divided by the respiratory rate."
- This is incorrect as it does not define alveolar ventilation.
- **Option C**: "Tidal volume times the respiratory rate."
- This is also incorrect because it represents minute ventilation, not specifically alveolar ventilation.
- **Option D**: "Minute ventilation plus the dead space."
- This is incorrect as it does not accurately describe alveolar ventilation.

4. **Conclusion**:
- The correct definition of alveolar ventilation is given by **Option A**, which states that it is the amount of air available for gas exchange in the lungs.

### Final Answer:
**The alveolar ventilation is the amount of air available for gas exchange in the lungs. (Option A)**

---