Please answer my question.

Dear student
Chlorine gas, iron, aluminium, iodine , carbon and sulphur powder are not compounds .
These are elements , elements is the  chemical entity consisting of atom or molecule in a form in which the substance is found naturally.

all others are compounds.

elements as ‘the basic form of matter that cannot be broken down into simpler substances by chemical reactions’. Iron, carbon, sulphur, mercury, oxygen etc. are the examples of elements.

Compounds are defined as the substances formed when two or more elements combine chemically in a fixed proportion. For example, water is a compound. It is formed when two atoms of hydrogen combine chemically with one atom of oxygen. This composition of water is constant throughout the universe, no matter where and how it is formed.

Regards