One mole of which hydrocarbon requires 8 mol o2 to achieve complete combustion to give carbon dioxide and water?

The typical structure of a hydrocarbon is HCnHnH where for every carbon atom, there's 2 hydrogen atoms plus a single hydrogen atom at each end of the hydrocarbon chain. So the expected output will be 1 CO2 molecule and 1 H2O molecule per carbon atom plus 1 extra H2O molecule. These molecules have to have a total of 16 oxygen atoms. So 2n + (n+1) = 16 where n = number of carbon atoms Solving for n gives 3n + 1 = 16 3n = 15 n = 5 So the equation should be: C5H7 + 8O2 ==> 5CO2 + 6H2O