Hi there! :)
Both are compounds.
[tex]CO_{2}[/tex] contains 1 carbon (C) atom and 2 oxygen (O) atoms.
It contains two different elements, so it is a COMPOUND.
[tex]Na_{2} O[/tex] is an IONIC compound with elements Sodium (Na) and Oxygen (O), which are different elements. Therefore, it is also a COMPOUND.
