They each contain a carbonyl group attached to a heteroatom with at least one lone pair. The alcohol contains neither a carbonyl or the extra heteroatom. Because these functional groups have very similar electronic and atomic arrangements, we expect them to have very similar chemical and physical properties. Any legitimate Lewis structure for sulfuric acid is acceptable in this case. Formal charges are considered a part of any Lewis structure, and must be included as well.
Bond polarity is a result of uneven distribution of the electron density within a covalent bond.
This is analyzed by considering the electronegativities of the bonded atoms. Oxygen is more electronegative than sulfur, so the bonding electron density is greater toward the oxygen. The slight negative charge that results on oxygen is designated with a d - . This leaves a deficiency of bonding electron density on the sulfur. The single most important factor that controls the geometry of any molecule or ion is electron repulsion.