Which out of `NH_(3) and NF_(3)` has higher dipole moment and why?

Explanation

`NH_(3)` has higher dipole moment than `NF_(3)`. Both `NH_(3)` and `NF_(3)` molecules have pyramidal shape with one lone pair on nitrogen atom. Fluorine is more electronegative that hydrogen and therefore, the `N-F` bonds should be more polar than `N-H` bonds. Consequently, the resultant dipole moment of `NF_(3)` should be much larger than that of `NH_(3)`. However, the dipole moment of ammonia `(mu=1.47D)` is larger than that of `NF_(3)(mu=0.24D)`. This is due to the presence of lone pair on nitrogen. In case of `NH_(3)`, the orbital dipole due to lone pair is in the same direction as the resulatnt dipole moment of the three `N-H` bonds. Therefore, it adds on the resultant dipole moment of the `N-H` bonds. On the hand, in case of `NH_(3)`, the orbital dipole is in the opposite direction to the sesultant dipole moment of the three `N-F` bonds. Thus, the lone pair moments cancel the resultant `N-F` bond moments as shown in figure.
Consequently, hte dipole moment of `NF_(3)` is low.