In a water molecule H2O , the oxygen atom is sp3 hybridized. To determine the hybridization, we can look at the electron configuration and the number of electron domains around the central atom. Oxygen has an electron configuration of 1s2s2p. In a water molecule, oxygen forms two sigma bonds with two hydrogen atoms and has two lone pairs of electrons. This gives a total of four electron domains around the oxygen atom. When there are four electron domains, the hybridization is sp3, which means one s orbital and three p orbitals are hybridized to form four sp3 hybrid orbitals. These sp3 hybrid orbitals are used for bonding with the hydrogen atoms and accommodating the lone pairs of electrons.