which compound contains only a nonpolar covalent molecule?\no o₂\no hcl\no h₂o\no no₃

Brief Explanations:

Non - polar covalent bonds occur between atoms with the same electronegativity. In $O_2$, two oxygen atoms have the same electronegativity, so the bond is non - polar. In $HCl$, $H_2O$ and $NO_3$, there are differences in electronegativity between the atoms, leading to polar bonds.

Answer:

A. $O_2$