In the NH4+ ion, the central atom is nitrogen N . To determine the hybridization of nitrogen, we need to look at its electron configuration and the number of electron domains around it.Nitrogen has 5 valence electrons. In NH4+, it forms four single bonds with four hydrogen atoms. This means that there are four electron domains bonding pairs around the nitrogen atom.According to the VSEPR theory, the electron domain geometry around the nitrogen atom is tetrahedral. To achieve this geometry, the nitrogen atom undergoes sp3 hybridization, which means it uses one s orbital and three p orbitals to form four sp3 hybrid orbitals. These hybrid orbitals then form sigma bonds with the hydrogen atoms.So, the hybridization of the central atom nitrogen in the NH4+ ion is sp3.