Which of the following does not act as buffer to maintain pH of blood?

Options

A. Carbonic acid
B. Monobasic phosphate
C. Dibasic phosphate
D. Myoglobin

Answer

To determine which of the following does not act as a buffer to maintain the pH of blood, we will analyze the known buffer systems in the body.

### Step-by-Step Solution:

1. **Identify the Buffer Systems in Blood**:
- The human body utilizes three primary buffer systems to maintain blood pH:
- **Bicarbonate Buffer System**: This system involves carbonic acid (H2CO3) and bicarbonate ions (HCO3-). It helps to regulate pH by neutralizing excess acids or bases.
- **Phosphate Buffer System**: This system consists of dihydrogen phosphate (H2PO4-) and hydrogen phosphate (HPO4^2-). It plays a role in buffering pH changes in the intracellular fluid and the kidneys.
- **Protein Buffer System**: Proteins, including hemoglobin, can act as buffers by binding to excess hydrogen ions (H+), thus helping to stabilize pH levels.

2. **Evaluate the Options**:
- We need to consider the options provided in the question. While the specific options are not listed in the question, we know that myoglobin is often mentioned in contrast to hemoglobin.
- **Myoglobin**: Myoglobin is a protein found in muscle tissue that carries oxygen but does not play a significant role in buffering blood pH.

3. **Conclusion**:
- Since myoglobin does not function as a buffer in the blood, the correct answer to the question is that myoglobin does not act as a buffer to maintain the pH of blood.

### Final Answer:
- The correct answer is **myoglobin** (option number four).