Oxidation of acetaldehyde with selenium dioxide produces:

When the aldehyde is oxidized with selenium dioxide, the methyl group of the acetaldehyde will convert into aldehyde group and the aldehyde group of the reactant will not be affected. So, the reactant given is acetaldehyde having formula 퐶퐻3퐶퐻푂. So, when it is oxidized, glyoxal will be formed. The reaction will be: 퐶퐻3퐶퐻푂+ 푆푒푂2 →푂퐻퐶−퐶퐻푂+ 푆푒+ 퐻2푂