Both and can be classified as pure substances because they have distinct properties and composition.

Both elements and compounds can be classifies as pure substances because they have distinct properties and composition.

Explanation:

Elements and compounds are considered as pure substances because both are always formed form are have same kind of atoms.

For example,

Carbon dioxide is compound. It always consist of one carbon atom and two oxygen atoms.

Water is compound it always have same kind of atoms two hydrogen and one oxygen that's why compounds are considered as pure substances.

Same is the case with elements. For example,

Hydrogen is element and it always consist of H atoms.

Iron is another element and it always have iron atoms.

So elements and compounds are always consist of same substances that's why they are considered as pure.

nacl is added to the aqueous of what? ? in order to get a proper answer you have to specify the exact composition of the aqueous solution.