Question

The net dipole moment of NF3 is less than that of NH3. Why? ​

Answer 1

In NH3, N is more electronegetive than H. So, N pulls the electrons from H towards itself and hence the direction of moment due to the N-H bonds is in the same direction as that of the lone pair of electrons on Nitrogen.

But on the other hand in the case of NF3 , F is more electronegative than N. So, all F atoms pull the electrons towards themselves. And, this resultant moment is opposite to the directions of that of the lone pair of electrons on the 'N' atom. And, since Dipole Moment is a vector quantity, the net dipole decreases.

Hope it Helps !!