Assertion : Life occurs upto 15,000 metres on the mountains.
Reason : Beyond 15,000 metres, temperature is too low, `CO_(2)` and `O_(2)` are too little.

Options

A. If both A and R are true and R is the correct explanation of A.
B. If both A and R are true but R is not the correct explanation of A.
C. If A is true but R is false.
D. If both A and R are false.

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that life occurs up to 15,000 meters on mountains. We need to evaluate whether this statement is true or false.

2. **Evaluating the Height of Life**: The highest point on Earth, Mount Everest, is approximately 8,848 meters. At such altitudes, the conditions are extremely harsh for life. Generally, life is not found beyond 8,000 meters due to lack of oxygen and extreme temperatures.

3. **Conclusion on the Assertion**: Since life cannot survive at 15,000 meters, the assertion is **false**.

4. **Understanding the Reason**: The reason provided states that beyond 15,000 meters, the temperature is too low and the levels of carbon dioxide (CO2) and oxygen (O2) are too low for life to exist.

5. **Evaluating the Reason**: This statement is true. At high altitudes, particularly beyond 8,000 meters, the temperature drops significantly, and the atmospheric pressure decreases, leading to lower availability of oxygen and carbon dioxide, which are essential for life.

6. **Conclusion on the Reason**: The reason is **true**.

7. **Final Evaluation**: Since the assertion is false and the reason is true, the overall conclusion is that the assertion does not support the reason. Therefore, the correct answer is that the assertion is false and the reason is true.