No, an element is not a mixture.
carbon is an element
No, oxygen is an element.
Nitrogen is not a mixture it's an element.
Heterogeneous mixture
Calcium is an element, so yes.
Gasoline is a mixture of various hydrocarbons, which are compounds.
Hydrogen is none of both, not being a mixture but an ELEMENT.
Sodium chloride (table salt) is a compound - NaCl.
Platinum (Pl) is not a mixture. It is an element. It consists only of itself.
copper is an ELEMENT therefore it is not a heterogeneous OR homogeneous mixture.
Iodine is an element, so a pure substance, not a mixture, (so even not homogeneous).
The ferric oxide is a chemical compound.