What number should be substituted for the question mark to balance the equation and why is that the correct number? 2C4H10 +?O2 → 8CO2 + 10H2O + heat Responses The number 9 is needed to balance the equation. The right side shows 8 oxygen atoms in carbon dioxide and 10 oxygen atoms in water for a total of 18 oxygen atoms. The number 9 is needed to balance the equation. The right side shows 8 oxygen atoms in carbon dioxide and 10 oxygen atoms in water for a total of 18 oxygen atoms. The numbe