Different opinions about the nature of two lone pairs on oxygen atom of carbonyl group in HCHO promote the present authors to undertake the study on this matter. Here opinions of different text books as stated by the authors are represented in brief and systematic manner to conclude finally that carbonyl oxygen may be sp hybridized with two different types of lone pairs as supported by M.O. theory and uv spectral data [one lone pair on py orbital and another lone pair on sp hybrid orbital] on oxygen atom.