In human blood a toxic substance called carbamino haemoglobin is formed by

Options

A. the combination of carbon dioxide with haemoglobin
B. the combination of carbon monoxide with haemoglobin
C. combination of methane with haemoglobin
D. combination of nitrogen with haemoglobin

Explanation

To solve the question about the formation of the toxic substance called carbaminohemoglobin in human blood, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Carbaminohemoglobin**:
- Carbaminohemoglobin is a compound formed when carbon dioxide (CO2) binds to hemoglobin in the blood. It is important to recognize that this compound is related to the transport of carbon dioxide from the tissues back to the lungs for exhalation.

2. **Identifying the Components**:
- The question provides four options regarding what combines with hemoglobin to form carbaminohemoglobin:
- A. Combination of carbon dioxide with hemoglobin
- B. Combination of carbon monoxide with hemoglobin
- C. Combination of methane with hemoglobin
- D. Combination of nitrogen with hemoglobin

3. **Analyzing Each Option**:
- **Option A**: This option states that carbaminohemoglobin is formed by the combination of carbon dioxide with hemoglobin. This is correct, as CO2 binds to hemoglobin to form carbaminohemoglobin.
- **Option B**: This option suggests that carbon monoxide (CO) combines with hemoglobin. While carbon monoxide does bind to hemoglobin, it forms carboxyhemoglobin, which is a different and more toxic compound. Thus, this option is incorrect.
- **Option C**: Methane (CH4) does not combine with hemoglobin in the blood, making this option incorrect.
- **Option D**: Nitrogen (N2) does not form any significant compound with hemoglobin in the blood, so this option is also incorrect.

4. **Conclusion**:
- After analyzing the options, it is clear that the correct answer is **A**: the combination of carbon dioxide with hemoglobin forms carbaminohemoglobin.

### Final Answer:
**A. Combination of carbon dioxide with hemoglobin**