which of these is a molecule and is also a compound?\no₂ (two atoms of oxygen joined together…

Brief Explanations:

A molecule is a group of two or more atoms held together by chemical bonds. A compound is a molecule that contains at least two different elements. $O_2$ is a molecule but consists of only oxygen atoms, so it is not a compound. $H_2O$ is a molecule made up of hydrogen and oxygen atoms, and since it has two different elements, it is also a compound.

Answer:

$H_2O$ (water with two atoms of hydrogen and one atom of oxygen joined together chemically)