# O_2 and H_2 are the same gas at what temperature?

$\text{O"_2}$ and $\text{H"_2}$ are pure substances. They are diatomic elements and will never be the same gas at any temperature. They can chemically combine with one another to form the compound water, $\text{H"_2"O}$, but that is a compound with very different properties compared to $\text{O"_2}$ and $\text{H"_2}$.