What number should be substituted for the question mark to balance the equation and why is that the correct number?


C3H8 +?O2 → 3CO2 + 4H2O + heat


A.

The number 7 is needed to balance the equation. The right side shows 3 oxygen atoms in carbon dioxide and 4 oxygen atoms in water for a total of 7 oxygen atoms.


B.

The number 3 is needed to balance the equation. The right side of the equation shows 6 oxygen atoms, so the left side needs 3 O2.


C.

The number 5 is needed to balance the equation. The right side of the equation shows 10 oxygen atoms, so the left side needs 5 O2.


D.

The number 4 is needed to balance the equation. The right side shows 4 oxygen atoms, so the left side needs 4 oxygen atoms.