The central atom in formaldehyde CH2O is carbon. To determine the hybridization, we need to consider the number of electron domains around the central atom. In formaldehyde, carbon forms two single bonds with two hydrogen atoms and a double bond with one oxygen atom.The number of electron domains is equal to the number of sigma bonds + the number of lone pairs. In this case, there are 3 sigma bonds 2 C-H bonds and 1 C-O bond and no lone pairs on the central carbon atom.According to the VSEPR theory, 3 electron domains correspond to sp2 hybridization. Therefore, the hybridization of the central carbon atom in formaldehyde CH2O is sp2.