Question

Which pair of molecules has the strongest dipole-dipole interactions?

Answer 1

Answer: NH3 and NH3

Explanation:

If hydrogen is bonded to a highly electronegative element, a strong dipole-dipole attraction is set up with strength ten times greater than normal dipole-dipole attractions, and it is crystal clear that electronegativity increase from left to right across the period and it decreases down the group. Nitrogen being electronegative more than Oxygen will exhibit a greater dipole-dipole attraction. As such, NH3 and NH3 is  the right answer.