Classification help

I need to classify each by either as a element, compound, homogeneous mixture or heterogeneous mixture. So far I have the following:

1. rust [iron(III) oxide]) - ?
2. diamond - ?
3. carbon dixoide - compound
4. air in a sealed flask - ?
5. vinegar and oil - ? heterogeneous mixture
6. water (pure) - compound
7. 14 carat gold - homogeneous mixture
8. unsaturated aqueous sodium choloride - ?

I am not sure of the ones with the ? could you give some help with explaination I would greatly appreciate it.

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Rust-compound [Red: Iron(III)Oxide, Green: Copper(II)Oxide or Iron(II)Oxide]
Diamond-element [Carbon in form of giant covalent structure]
Sealed air-homogenous mixture [you cannot [color=blue]see[/color] the difference between gases]
unsaturated aqueous sodium choloride-homogenous mixture [all liquid solutions which are has concentration under or equal to saturation are homogenous]
vinegar+oil- heterogenous [they don't actually mix together into a single stuff]

Thanks.

Appreciate the input very good explainations.

Thanks for your appreciation. I'm really grateful.

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