2Ethane(C2H6) + 7oxygen (O2) ----> 4Carvon dioxide + 6Water
60g 224g 176g 108g
no. of moles of O2 = 11.2g/32
Volume of O2 = 11.2 x 22.4/32 = 7.84 L Ans
Sorry I couldn't write the chemical reaction with symbols but I have written it as balanced chemical reaction.
Explanation - As you can see from the balanced chemical equation 60 g ethane requires 224 g of oxygen . So, by unitary method 1 g ethane requires (224/60) g oxygen and 3 g ethane requires (224 x 3 / 60) g oxygen , i.e., 11.2 g oxygen.