# How to find bond angle of NH3,(BF4)-?

For both $N {H}_{3}$ and $B {F}_{4}^{-}$ electronic geometry is TETRAHEDRAL to a first approximation. For $B {F}_{4}^{-}$...molecular geometry is TETRAHEDRAL...and $\angle F - B - F \equiv {109.5}^{\circ}$...
For ammonia, the lone pair of electrons influences molecular geometry. $N {H}_{3}$ is trigonal planar with $\angle H - N - H \equiv {104.5}^{\circ}$, i.e. compressed slightly with respect to the tetrahedron.