What is the hybridization of H2O?

The oxygen atom in the H2O molecule is sp3 hybridized. This is because when oxygen is bonded with two molecules, like it is in water, the three 2p orbitals and the 2s orbital combine to create four sp3 hybrid orbitals.

To make water, the oxygen atom forms a covalent bonds with each hydrogen atom. Covalent bonds are when two atoms share electrons to form a strong bond. Oxygen's other electron pairs go into nonbonding orbitals. The nonbonding electron pairs still take up space and exert force on the other orbitals, so instead of being flat, the hydrogen-oxygen-hydrogen bond angle in water is 105 degrees. This bond geometry is called distorted tetrahedron.