Answer
a. dispersion force and dipole-dipole forces
b. dispersion force, hydrogen bonds, and dipole-dipole forces
c. dispersion forces
d. dispersion forces
Work Step by Step
a. In $HCl$, polar bond exists in this molecule because of the difference in electronegativities of atoms in $HCl$. Hence dispersion force and dipole-dipole forces are present in $HCl$.
b. In $H_{2}O$, a polar bond exists in this molecule because of the difference in electronegativities of atoms in $H_{2}O$. Hydrogen is bonded to oxygen. Hence dispersion force, hydrogen bonds, and dipole-dipole forces are present in $H_{2}O$.
c. $Br_{2}$ is a nonpolar molecule. Hence only dispersion forces are present.
d. $He$ is a nonpolar molecule. Hence only dispersion forces are present.
