The central oxygen atom is a state of sp3 hybridization having only one available lone pair.
<h3>What is hybridization?</h3>
The term hybridization refers to the mixing of two or more atomic orbitals to yield hybrid orbitals that are suitable for bonding.
Looking at the ion H3O^+, we can see that the central oxygen atom is a state of sp3 hybridization having only one available lone pair. The image of the ion is shown here.