Whats the difference between diatomic and poly-atomic molecules. with examples

A polyatomic molecules is a molecule that is composed of more than one element. The elements in this molecule are chemically bonded and has a net charge that is neutral like an ion. Example are CO2 and H2O. On the other hand, diatomic molecule is a molecule that is composed of two same atoms which are bonded covalently. An example is oxygen, it exist as O2.

They are all decomposition reactions.

257 grams h2o i think