What is the mole ratio of O2 to C4H9OH?

To determine the mole ratio of O2 to C4H9OH, we need to look at the balanced chemical equation for the combustion of butanol (C4H9OH). The balanced equation is:

[ C4H9OH + 6 O2 \rightarrow 4 CO2 + 5 H2O. ]

From the equation, the mole ratio of O2 to C4H9OH is 6:1. Thus, for every mole of butanol, six moles of oxygen are required.