Final answer:
The geometry around the oxygen atom in the hydroxyl group of a carboxylic acid is tetrahedral. This is due to two bonds and two lone pairs of electrons according to VSEPR theory, while the central carbon of the carboxyl group is trigonal planar.
Step-by-step explanation:
The shape around the oxygen atom in the hydroxyl group of a carboxylic acid is tetrahedral. When considering the structural geometry of molecules like carboxylic acids, the oxygen atom in the hydroxyl group (-OH) forms two single bonds, one with a hydrogen atom and the other with the central carbon atom of the carboxylic group. Additionally, the oxygen has two lone pairs of electrons. According to VSEPR (Valence Shell Electron Pair Repulsion) theory, this arrangement leads to a tetrahedral geometry to minimize repulsion between these pairs of electrons.
In contrast, the geometry around the central carbon atom of the carboxyl group is trigonal planar, as dictated by its double bond with the oxygen atom (C=O) and single bonds with the other oxygen (hydroxyl group) and the rest of the molecule. The trigonal planar geometry is due to the arrangement of three groups around the central carbon atom, with 120° angles between each pair.