All the following factors are favourable for the formation of oxyhaemoglobin, except

Options

A. Low `CO_2`
B. Low `H^(+)` concentration
C. Low `O_2` tension
D. Low temperature

Answer

To solve the question regarding the factors that favor the formation of oxyhemoglobin, we need to analyze each of the options provided:

1. **Understanding Oxyhemoglobin Formation**:
- Oxyhemoglobin is formed when hemoglobin binds with oxygen. This process is influenced by various factors including the partial pressure of oxygen, carbon dioxide levels, hydrogen ion concentration, and temperature.

2. **Analyzing Each Option**:
- **Option A: Low CO2**:
- Low levels of carbon dioxide (CO2) favor the formation of oxyhemoglobin. When CO2 levels are low, the affinity of hemoglobin for oxygen increases, promoting the binding of oxygen.
- **Option B: Low H+ concentration**:
- A low concentration of hydrogen ions (H+) corresponds to a higher pH (less acidic), which also favors the formation of oxyhemoglobin. High acidity (high H+ concentration) would reduce the affinity of hemoglobin for oxygen.
- **Option C: Low oxygen tension**:
- Low oxygen tension means there is a low partial pressure of oxygen. This condition does not favor the formation of oxyhemoglobin; instead, it promotes the release of oxygen from hemoglobin (dissociation).
- **Option D: Low temperature**:
- Low temperatures favor the binding of oxygen to hemoglobin. Higher temperatures would promote the release of oxygen.

3. **Conclusion**:
- Among the options provided, the only factor that does not support the formation of oxyhemoglobin is **C: low oxygen tension**. This is because low oxygen tension leads to a decreased affinity of hemoglobin for oxygen, promoting dissociation rather than association.

### Final Answer:
**C: Low oxygen tension**