H2O is a molecule of water, which consists of two hydrogen atoms and one oxygen atom. OH2 is a hydroxyl radical, which consists of one hydrogen atom and one oxygen atom with an unpaired electron.

The main difference between H2O and OH2 is that H2O is a neutral molecule, while OH2 is a free radical. This means that OH2 has an unpaired electron, which makes it highly reactive and capable of participating in a variety of chemical reactions.

In contrast, H2O is a relatively stable molecule that does not readily participate in chemical reactions. This is because the oxygen atom in H2O is bonded to two hydrogen atoms, which makes it difficult for other molecules to react with it.

As a result of their different properties, H2O and OH2 play different roles in the environment. H2O is essential for life and is found in all living organisms. OH2, on the other hand, is a reactive species that can be harmful to living organisms if it is present in high concentrations.