Diatomic molecules of gases are due to bonds.

covalent.

Explanation:

The difference in electronegativity between atoms in the molecule indicates the type of bond between the molecules.If the difference between the electronegativity from 0 to 0.4, this means that the bond is non-polar covalent bond.In a diatomic molecules, the molecule has atoms of the same type, so the difference in electronegativity between the atoms is zero.Thus, the bond in a diatomic molecule is covalent bond.For example, H₂, O₂, Cl₂, ...etc.