Elements are pure substances made up of atoms with the same atomic number. Based on the options you provided:
1. C - This is an element, representing carbon.
2. CO2 - This is a compound composed of two different elements, carbon (C) and oxygen (O). So, it's not an element itself.
3. H2Oo - This appears to be a typo or an incorrect representation. H2O is the chemical formula for water, composed of the elements hydrogen (H) and oxygen (O).
4. Au - This is an element, representing gold.
So, elements in your list are C and Au. CO2 is a compound, and H2Oo is not a valid representation.