The geometry of ammonia molecule can be best described as

nitrogen at one vertex of a regular tetrahedron, the other three vertices being occupied by the three hydrogens

nitrogen at the center of the tetrahedron, three of the vertices being occupied by three hydrogens

nitrogen at the center of an equilateral triangle, three corners being occupied by three hydrogens

nitrogen at the junction of a $\mathrm{T}$, three open ends being occupied by three hydrogens