Which of the following is a characteristic of a trigonal pyramidal geometry?

Trigonal pyramidal geometry is characterized by a central atom surrounded by three substituents (atoms or groups) and one lone pair of electrons. In this arrangement, the three substituents occupy the corners of a pyramid with the central atom at the apex. The presence of the lone pair affects the spatial arrangement, creating a pyramidal shape rather than a flat one, which is typical of trigonal planar arrangements where all substituents are bonded.

For example, ammonia (NH₃) exhibits a trigonal pyramidal geometry due to its three hydrogen atoms bonded to nitrogen and one lone pair of electrons on the nitrogen atom. This lone pair exerts a repulsive force that pushes the hydrogen atoms closer together, resulting in the three-dimensional pyramidal shape.

In contrast, the other choices do not fit this description. One option describes a configuration with four substituents, which corresponds to a tetrahedral geometry. Another involves two substituents and two lone pairs, leading to a bent geometry, while the last option depicts one substituent with three lone pairs, resulting in a linear shape. Therefore, having three substituents and one lone pair distinctly defines the trigonal pyramidal geometry.