What is para and ortho hydrogen?
At the room temperature, the ratio of ortho- to para-hydrogen is at its maximum of 3 : 1. Even at very high temperatures, the ratio of ortho- to para-hydrogen can never be more than 3 : 1. So, it is possible to get pure para hydrogen by cooling ordinary hydrogen gas to a very low temperature (close to 20 K) but it is never possible to get a sample of hydrogen containing more than 75% of ortho hydrogen.