Even though both `NH_(3) " and " NF_(3)` are pyramidal, `NH_(3)` has a higher dipolemoment compared to `NF_(3)`. Why ?

Explanation

Both `NH_(3) " and " NF_(3)` have pyramidal shape with a lone pair of electrons on nitrogen atom. Although fluorine is more electronegative than nitrogen, the resultant dipolemoment in `NH_(3)` is greater than in `NF_(3)`.
In the case of `NH_(3)` the orbital dipolemoment due to the lone pair electrons and the resultant dipolemoment of the three N - H bonds are acting in the same direction. This enchances the dipolemoment of molecule.

In `NF_(3)` the orbital dipolemoment is in the direction opposite to the resultant dipolemoment of the three N - F bonds. The orbital dipolemoment due to lone pair electrons decreases this effect of the resultant N - F bond moments. This results in the decrease of dipolemoment in `NF_(3)` than in `NH_(3)`.