If 4.20 mol of ethane, c2h6, undergo combustion according to the unbalanced equation given below, how many moles of oxygen are required?

The Balance Chemical equation for said reaction is as follow,

                         C₂H₆   + 3.5 O₂    →    2 CO₂  +  3 H₂O
Or,
                        2 C₂H₆   + 7 O₂    →    4 CO₂  +  6 H₂O

According to equation,

        2 moles of Ethane react completely with  =  7 moles of Oxygen

So,

               4.20 moles of Ethane will react with  =  X moles of Oxygen

Solving for X,

                             X  =  (4.20 mol × 7 mol) ÷ 2 mol

                             X  = 14.7 moles of Oxygen

Result:
            14.7 moles of Oxygen are required to react with 4.20 moles of Ethane for complete reaction.