Final answer:
Para hydrogen is more stable than ortho hydrogen due to its lower energy state, as the spins of the hydrogen nuclei are oppositely aligned in para hydrogen, whereas they are aligned in the same direction in ortho hydrogen.
Step-by-step explanation:
The stability of ortho and para hydrogen is determined by their spin states. Ortho hydrogen consists of hydrogen molecules where the spins of the two hydrogen nuclei (protons) are aligned in the same direction, which is a higher energy arrangement. On the other hand, in para hydrogen, the spins are aligned oppositely, resulting in a lower energy state that is more stable.
At room temperature, a mixture of both forms exists, but as the temperature decreases, para hydrogen becomes more prevalent due to its lower energy state. Furthermore, the interconversion between ortho and para hydrogen is a slow process, mediated by a catalyst or magnetic field, because it involves a change in the nuclear spin, which is a quantum mechanical property.
Therefore, para hydrogen is considered more stable because it has a lower energy state compared to ortho hydrogen. This concept ties into the general rule that a molecule or atom is more stable when it is in its lowest possible energy state.