What is the approximate normal composition of alveolar air ?

Options

A. `14%` oxygen, `6%` carbon dioxide, `80%` nitrogen
B. `21%` oxygen, `2%` carbon dioxide, `77%` nitrogen
C. `16%` oxygen, `3%` carbon dioxide, `81%` nitrogen
D. `10%` oxygen, `8%` carbon dioxide, `82%` nitrogen

Answer

To determine the approximate normal composition of alveolar air, we can follow these steps:

### Step 1: Understand the Components of Alveolar Air
Alveolar air consists mainly of three gases: oxygen (O₂), carbon dioxide (CO₂), and nitrogen (N₂).

### Step 2: Analyze the Given Options
We have four options for the composition of alveolar air:
1. 14% O₂, 6% CO₂, 80% N₂
2. 21% O₂, 2% CO₂, 77% N₂
3. 16% O₂, 3% CO₂, 81% N₂
4. 10% O₂, 8% CO₂, 82% N₂

### Step 3: Identify Normal Values
In a healthy individual, the normal composition of alveolar air is approximately:
- Oxygen: around 14% (it can vary slightly, typically around 13.7% to 14%)
- Carbon Dioxide: around 5% to 6% (often cited as approximately 5.2%)
- Nitrogen: the remaining percentage, which is typically around 80% (often around 79% to 81%)

### Step 4: Compare Each Option
- **Option 1**: 14% O₂, 6% CO₂, 80% N₂ - This is consistent with normal values.
- **Option 2**: 21% O₂, 2% CO₂, 77% N₂ - This is more representative of atmospheric air, not alveolar air.
- **Option 3**: 16% O₂, 3% CO₂, 81% N₂ - The oxygen percentage is higher than expected for alveolar air.
- **Option 4**: 10% O₂, 8% CO₂, 82% N₂ - The oxygen percentage is too low, and carbon dioxide is too high for normal alveolar air.

### Step 5: Conclusion
Based on the analysis, the correct answer for the approximate normal composition of alveolar air is **Option 1: 14% O₂, 6% CO₂, 80% N₂**.

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