To determine how many atoms of carbon (C) are present in the reactants of the given chemical equation:
C7H16 + O2 → CO2 + H2O
We look only at the reactants, which are C7H16 and O2.
In C7H16, there are 7 carbon atoms. O2 does not contain any carbon atoms.
Therefore, the total number of carbon atoms in the reactants is 7.
So, the correct response is:
7 atoms