Which of the following exhibits the weakest intermolecular forces?

He

The correct answer is option 3. He.

There are three major intermolecular forces that act on the compound such as; London dispersion forces, Dipole-Dipole interactions, and hydrogen bonding.
Among those, the London dispersion forces are the weakest while hydrogen bonding is the strongest of all.
Hydrogen bonding is formed by the elements N, O, F when attached to H. So, here in the case of H₂O and NH₃ hydrogen bonding is present.

In the case of HCl, we have a dipole-dipole interaction present due to the electronegativity difference between H and Cl.

Helium is the noble gas element and there are no attractive forces that exist in them except London dispersion. So, He has London dispersion force which is the weakest intermolecular force.