Question

how many moles of oxygen are needed for the combustion of one mole of cyclohexane

Answer 1

Ciclohexane has the molecular formula C₆H₁₂ so the overall reaction will be:

C₆H₆ + O₂ ----------> CO₂ + H₂O

Balancing this reaction:

2C₆H₆ + 15O₂ ----------> 12CO₂ + 6H₂O or   C₆H₆ + 15/2O₂ ----------> 6CO₂ + 3H₂O

So, in this case we'll use the second balanced reaction (although you may use the first one and the result will be the same)

1 mole of C₆H₆ needs 15/2 moles of O₂ which would be:

moles of O₂ = 1 * 15/2 = 7.5 moles of O₂

Hope this helps