C. Balance these fossil-fuel combustion reactions. (1 point)

The question is incomplete. The complete question is :

C. Balance these fossil-fuel combustion reactions. (1 point)

C8H18(g) + 12.5O2(g) →    CO2(g) + 9H2O(g) + heat

CH4(g) + O2(g) →     CO2(g) + H2O(g) + heat

C3H8(g) + O2(g) →    CO2(g) + H2O(g) + heat

C6H6(g) + O2(g)  →   CO2(g) + H2O(g) + heat

Solution :

C8H18(g) + 12.5O2(g) →    __8__CO2(g) + 9H2O(g) + heat

When 1 part of octane reacts with 12.5 parts of oxygen, it gives 8 parts of carbon dioxide and 9 parts of water along with liberation of energy.

CH4(g) + __2__O2(g) →     __1__CO2(g) + __2__H2O(g) + heat

When 1 part of methane reacts with 2 parts of oxygen, it gives 1 part of carbon dioxide and 2 parts of water along with liberation of energy.

C3H8(g) + __5__O2(g) →    __3__CO2(g) + __4__H2O(g) + heat

When 1 part of propane reacts with 5 parts of oxygen, it gives 3 part of carbon dioxide and 4 parts of water along with liberation of energy.

C6H6(g) + __1/2__O2(g)  →   __6__CO2(g) + __3__H2O(g) + heat

When 1 part of propane reacts with 1/2 parts of oxygen, it gives 6 part of carbon dioxide and 3 parts of water along with liberation of energy.

the answer is c.the valence of the atoms combine .