Which of the following statement is true about RBCs in humans?

Options

A. They carry about `20-25` percent of `CO_(2)`.
B. They transport `99.5` percent of `O_(2)`
C. They transpart about `80` per cent oxygen only and the rest `20` percent of it is transported in dissolved state in blood plasma.
D. They do not carry `CO_(2)` at all.

Explanation

To determine which statement about RBCs (Red Blood Cells) in humans is true, we can analyze the provided information step by step.

### Step-by-Step Solution:

1. **Understand the Role of RBCs**:
- RBCs are primarily responsible for the transport of gases in the blood. They carry oxygen from the lungs to the tissues and carbon dioxide from the tissues back to the lungs.

2. **Identify the Percentage of Gases Transported**:
- RBCs transport approximately 97% of oxygen and about 20 to 25% of carbon dioxide. The remaining carbon dioxide is transported in other forms, such as dissolved in plasma or as bicarbonate ions.

3. **Evaluate Each Statement**:
- **Statement 1**: "They carry about 20 to 25% of Carbon Dioxide."
- This statement is **true** based on the information provided.
- **Statement 2**: "They transport 99.5% of Oxygen."
- This statement is **false** because RBCs transport about 97% of oxygen.
- **Statement 3**: "They transport 80% of oxygen."
- This statement is also **false** as RBCs transport 97% of oxygen, not 80%.
- **Statement 4**: "They do not carry carbon dioxide at all."
- This statement is **false** because RBCs do carry carbon dioxide.

4. **Conclusion**:
- The only true statement regarding RBCs in humans is the first one: "They carry about 20 to 25% of Carbon Dioxide."

### Final Answer:
The true statement about RBCs in humans is: **They carry about 20 to 25% of Carbon Dioxide.**

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