Answer: Option (d) is the correct answer.
Explanation:
When two atoms are bonded together then it is known as a diatomic molecule.
Such as nitrogen exists as [tex]N_{2}[/tex] molecule in atmosphere so, it is a diatomic molecule.
Hydrogen also exists as [tex]H_{2}[/tex] molecule in atmosphere so, it is also a diatomic molecule. Also, bromine is a diatomic molecule because it exists as [tex]Br_{2}[/tex] molecule into the atmosphere.
But helium exists as He molecule as it has 2 electrons so, as per the octet rule it's s-shell is completely filled. Hence, it is stable and exists as a monoatomic molecule into the atmosphere.
Thus, we can conclude that out of the given options, helium is not a diatomic molecule.
