Pure para-hydrogen is available but not pure orthohydrogen. Explain.

Explanation

At ordinary temperature, ordinary hydrogen is a mixture of 75% of ortho and 25% of para-isomer. With decrease in temperature, amount of ortho-hydrogen decreases while that of para-hydrogen increases. At 20K pure, para-hydrogen is obtained. As para-hydrogen is more stable, it is found in the pure form. However, if temperature is increased, the amount of ortho-isomer of dihydrogen increases but at 400 K or above, the ratio of ortho-and para-isomer is fixed (3:1). Therefore, pure para-hydrogen is available but not pure ortho-hydrogen.