CHEMISTRY:complete combustion?

Question

What mass of oxygen is consumed by the complete combustion of 23.0 grams of ethylene?

C2H4(g) + 3 O2(g) → 2 CO2(g) + 2 H2O(g)

a.8.75 g
b.69.0 g
c.78.7 g
d.26.2 g
e.60.5 g

is it answer a?
thanks

Answer 1

carbon: 12.01 amu
hydrogen 1.008 amu

so C2H4 = 28.052 grams per mole

oxygen: 15.9994 amu

so 3 O2 = 95.9964 grams per mole

95.9964 / 28.052 x 23.0 g = 78.7 g

So the answer is [ c. ]

Answer 2

b.

You have 23/32 moles of C2H4 each mole reacts with 3 mol O2 that's 3(23/32) mols of O2, which weighs 3(23/32)32 g or 69g.