Oxygen in expired air

Options

A. `10%`
B. `16%`
C. `19%`
D. `4%`

Answer

To determine the percentage of oxygen in expired air, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Composition of Air**:
- The air we breathe in (inhaled air) is composed of approximately 78% nitrogen, 21% oxygen, and trace amounts of other gases including carbon dioxide.

2. **Recognize Changes in Composition After Respiration**:
- When air is inhaled, oxygen is utilized by the body for metabolic processes, and carbon dioxide is produced as a waste product.

3. **Identify the Composition of Expired Air**:
- After the process of respiration, the composition of the air that is exhaled (expired air) changes.
- The typical composition of expired air includes:
- Approximately 78.04% nitrogen
- Approximately 16% oxygen
- Approximately 4-5% carbon dioxide
- About 1% of other gases

4. **Select the Correct Percentage of Oxygen**:
- From the information gathered, we see that the percentage of oxygen in expired air is around 16%.

5. **Choose the Correct Option**:
- Given the options (10%, 16%, 19%, or 4%), the correct answer is 16%.

### Final Answer:
- The percentage of oxygen in expired air is **16%** (Option B).

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