Assertion : The presence of CO reduces the amount of haemoglobin available in the blood for carrying oxygen to the body cells.
Reason : CO combines with haemoglobin about 200 times less easily than oxygen to form complex.

Options

A. Assertion and reason both are correct statements and reason is correct explanation for assertion.
B. Assertion and reason both are correct statements but reason is not correct explanation for assertion.
C. Assertion is correct statement but reason is wrong statement
D. Assertion is wrong statement but reason is correct statement.

Answer

### Step-by-Step Text Solution:

1. **Understanding the Assertion**: The assertion states that the presence of carbon monoxide (CO) reduces the amount of hemoglobin available in the blood for carrying oxygen to body cells. This is true because CO binds to hemoglobin more effectively than oxygen does, which prevents oxygen from binding.

2. **Understanding the Reason**: The reason given is that CO combines with hemoglobin about 200 times less easily than oxygen to form a complex. This statement is incorrect. In fact, CO binds to hemoglobin about 200 times more easily than oxygen, forming a stable complex known as carboxyhemoglobin.

3. **Conclusion**: Since the assertion is true and the reason is false, we can conclude that the assertion is correct, but the reason provided is incorrect.

### Final Answer:
- **Assertion**: True
- **Reason**: False