C818 + _ 02 → __CO2 + __ H2O

2C₈ H₁₈   +  25O₂   →  16CO₂     +    18H₂O

Explanation:

The given expression:

         C₈ H₁₈   +  O₂   →  CO₂     +    H₂O

We need to balance the expression so that mass is conserved.

One approach is to use a mathematical method;

       aC₈ H₁₈   + b O₂   →  cCO₂     +   d H₂O

a, b , c and d are the coefficients that will balance the expression:

  Conserving C;

               8a = c

    Conserving H;

               18a  = 2d

   Conserving O;

                2b  = 2c + d

Now let a = 1;

             c  = 8

              d  = 9

         2b  = 2(8) + 9

         2b  = 25

           b =  

Multiply through by 2 to give whole numbers:

              a  = 2, b = 25, c  = 16, d  = 18

     2C₈ H₁₈   +  25O₂   →  16CO₂     +    18H₂O

the answer would be a