(i) → (c) (ii) → (d) (iii) → (a) (iv) → (b)

The halogen derivatives are matched to their pharmaceutical applications. Chloramphenicol is an antibiotic used in treatment of typhoid fever, thyroxine is a hormone whose dysregulation causes goiter, chloroquine is a drug used in treatment of malaria, and chloroform is used as an anesthetic in some cases.