Answer:
When molecules have permanent dipole moments
Step-by-step explanation:
When molecules have permanent dipole moment then two molecules will apply force on each by interacting with the electric field of each other
As we know that electric field due to dipole on its axial position is given as


now we know that since the dipole is having positive and negative charge separated by some distance so here when one dipole is placed in electric field of other dipole then due to this field charge interaction the force between them is significant.
so correct answer will be
When molecules have permanent dipole moments