Classify the carbohydrate tagatose by both the carbonyl group and the number of carbon atoms. There is a Fischer projection for D-tagatose. The carbon chain is depicted vertically, with a CH2OH group bonded to a CO group at the top and a CH2OH group at the bottom, while the three remaining carbon atoms are represented by the center of crossing lines. The tagatose molecule has all hydroxyls but the third one (from top to bottom) on the left and hydrogens opposite to them.