Answer:
CO2(down)
Explanation:
The atomic symbol can have one letter or more. Always the first letter is in uppercase. For example, Iron has the symbol Fe. And in a molecule it is followed by the number of atoms, this number is placed as a sub-index (down). Carbon is represented by the symbol C and oxygen by the letter O. That is why the molecule formed by one atom of carbon and two atoms of oxygen is written CO2 (down).
