Conc of `CO_(2)` is lowest in

Options

A. Anatomical dead space after expiration
B. The alveoli at the end of inspiration
C. In blood after inspiration
D. Anatomical dead space after inspiration

Answer

To determine where the concentration of carbon dioxide (CO₂) is lowest in the body, we need to analyze the options provided and understand the processes of respiration and gas exchange.

### Step-by-Step Solution:

1. **Understanding the Respiratory System**: The respiratory system is primarily composed of the lungs, where gas exchange occurs. The alveoli, tiny air sacs in the lungs, are the main sites for this exchange.

2. **Gas Exchange Process**: During gas exchange, oxygen from the atmosphere is taken in, and carbon dioxide produced by the body’s tissues is expelled. The concentration of CO₂ varies in different parts of the respiratory system and the body.

3. **Analyzing the Options**:
- **Option A: Anatomical Dead Space**: This refers to the parts of the respiratory system (like the trachea and bronchi) where air does not participate in gas exchange. The air here is not involved in the exchange of gases, so it does not accumulate CO₂.
- **Option B: Alveoli**: In the alveoli, after inhalation, the concentration of CO₂ is around 40 mmHg, as it is the site of gas exchange where CO₂ is expelled from the blood.
- **Option C: Blood**: The concentration of CO₂ in deoxygenated blood is approximately 45 mmHg, which is higher than in the alveoli because it carries CO₂ from the tissues to the lungs.
- **Option D: Atmospheric Air**: The concentration of CO₂ in atmospheric air is about 0.3 mmHg, which is significantly lower than in any other part of the body.

4. **Conclusion**: After analyzing the options, we find that the concentration of CO₂ is lowest in the atmospheric air, which is inhaled into the anatomical dead space. Therefore, the correct answer is **Option D: Atmospheric Air**.