Which of the following is not an example of a compound? A substance comprised of:

atoms of the same element

atoms of two different elements

positive particles of one element attracted to negative particles of a different element

positive particles of one element attracted to negative groups of atoms of other elements

Answer: atoms of the same element.

Justification:

There are two kinds of pure substances: elements and compounds.

Elements are pure substances consiituted by one kind of atoms. They cannot be divided into simpler substances either by physical or chemical means. This leads you to the answer of the question: atoms of the same element is not an example of compound, but of elements.

On the other hand, a compound is a chemical combination of two or more different atoms. The compounds can be splited into simpler substances (the elements) by chemical means.

Hence, second, third, and fourth choices are all examples of compound: they are pure substances of two or more kind of atoms.