If you are asking the field in M.Sc you can apply after B.Sc in Chemistry, There are several specializations in the field of chemistry from which a student can choose for their higher studies. The options for higher studies are

M.Sc. Chemistry

M.Sc. Analytical Chemistry

M.Sc. Drug Chemistry

M.Sc. Organic Pharmaceutical Chemistry

M.Sc. Physical & Materials Chemistry

In case you have any other query then let me know.