Which of the following situations would a dipole-dipole forces be significant?
when molecules have permanent dipole moments,
when molecules are nonpolar,
when van der waals forces are also present,
when van der waals forces are present

When molecules have permanent dipole moments

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

so easy. just google the electromagnetic waves and it’ll pop up.