Which of the following is not correct about carbon monoxide?

Options

A. It forms carboxyhaemoglobin
B. It reduces oxygen carrying ability of blood
C. The carboxyhaemoglobin (haemoglobin bound to CO) is less stable than oxyhaemoglobin
D. It is produced due to incomplete combustion

Answer

To solve the question "Which of the following is not correct about carbon monoxide?", we need to analyze each of the given options regarding carbon monoxide (CO) and determine which statement is incorrect.

### Step-by-Step Solution:

1. **Option 1: It forms carboxyhemoglobin.**
- Carbon monoxide binds with hemoglobin in the blood to form carboxyhemoglobin (COHb). This is a well-known fact and is indeed correct. Therefore, this option is true.

**Hint:** Remember that carboxyhemoglobin is formed when CO binds to hemoglobin, and it is a significant health hazard.

2. **Option 2: It reduces the oxygen-carrying ability of blood.**
- Carbon monoxide competes with oxygen for binding sites on hemoglobin. When CO binds to hemoglobin, it prevents oxygen from binding, thereby reducing the blood's ability to carry oxygen. This statement is also correct.

**Hint:** Consider how CO affects hemoglobin's ability to transport oxygen in the bloodstream.

3. **Option 3: The carboxyhemoglobin that is hemoglobin bound to CO is less stable than oxyhemoglobin.**
- This statement is incorrect. Carboxyhemoglobin is actually more stable than oxyhemoglobin. Once CO binds to hemoglobin, it does not easily release, making it a stable and dangerous compound. Therefore, this option is the one that is not correct.

**Hint:** Compare the stability of carboxyhemoglobin with oxyhemoglobin; think about the implications of their binding affinities.

4. **Option 4: It is produced due to incomplete combustion.**
- Carbon monoxide is indeed produced during the incomplete combustion of carbon-containing fuels. This statement is correct.

**Hint:** Recall the conditions under which CO is formed and how it differs from complete combustion products.

### Conclusion:
The statement that is not correct about carbon monoxide is **Option 3: The carboxyhemoglobin that is hemoglobin bound to CO is less stable than oxyhemoglobin.**