To burn 1 molecule of c7h16 to form co2 and h2o (complete combustion), how many molecules of o2 are required?

The complete balanced chemical reaction is:

C7H16  +  3O2  -->  7CO2  +  8H2O

So 3 moles of oxygen O2 is required for every 1 mole of C7H16. In the same manner, 3 molecules of O2 is required for every 1 molecule of C7H16.

3 molecules O2