Rank the following groups in terms of their priority according to the Cahn-Ingold-Prelog system of priorities. Give the highest ranking group a priority of 1 and the lowest ranking group a priority of 4.
a. D
b. H
c. NH2
d. CH2OH

Explanation:

Cahn, Ingold, and Prelog formulated a rule to specify the arrangement of the atoms or groups that are present in an asymmetric molecule. This rule is called a Cahn-Ingold-Prelog system. This system is generally used in the R, S system of nomenclature.

          According to this rule, such an atom that is directly linked to the asymmetric carbon atom is given the highest priority that has the highest atomic number. So here  Nitrogen atom of molecule is given the highest priority because Nitrogen has 7 atomic numbers. Carbon atom of molecule  has 6 atomic number. So it is given 2nd position. Deuterium and Hydrogen have 2 and 1 atomic numbers respectively so the are given 3rd and 4th order respectively.