Which of the following are not compounds?

(a) Chlorine gas

(b) Potassium chloride

(c) Iron

(d) Iron sulphide

(e) Aluminium

(f) Iodine

(g) Carbon

(h) Carbon monoxide

(i) Sulphur powder

These are not compounds:
(a) Chlorine gas
Chlorine gas consists of chlorine molecules. Chlorine is a non-metal.

(c) Iron

Iron is a metal.
(e) Aluminium

Aluminum is a metal

(f) Iodine
Iodine is a non-metal.
(g) Carbon

Carbon is a non-metal.

(i) Sulphur powder

Suphur is a non-metal.

Others are compounds because they are formed by the combination of different elements.