Correct Answer - C
A priority sequence (proposed by Cahn, Ingold and Prelog) is assogned to the four ligands bonded to the chiral center. The directly-bonded atom having the highest atomic number has the highest priority and the other ligand atoms follow in order of decreasing atomic numbers. When two ligands are istopes, i.e., `H`and `D`, the one with the higher atomic mass has the higher priority. Thus `-OH` bonded through oxygen atom (higher atomic number than carbon atom) has the highest priority. Since other ligands have a `C` bonded to the chiral center, the priority is determined by moving to the next atom in the chain. In the case of `-CH_(2)OH` these are `O,H` and `H`. Where there is a multiple bond, the multiply-bonded atoms are counted twice for a double bond and three times for a triple bond. Thus `-overset(O)overset(||)C-OH(O,O,O)` has priority over `-CH =O (O,O H)`. Thus the correct order of decreasing prioity is
`-OH gt - COOH gt -CHOgt -CH_(2)OH`
