The word Aztecs is a proper noun, because it is a name of a certain nation.
Common nouns are words such as table, chair, desk, etc. Compound noun is just a noun that has more than one word, such as brother-in-law. Collective noun is a noun such as deer, sheep, etc.
The word who can only be used when it is the subject of a verb. If you are unsure which to use, use who. Firstly, it is much more common than whom.<span>
Hope this helps:)
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