дано
V(C2H6) = 10 L
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V(возд)-?
2C2H6+7O2-->4CO2+6H2O
n(C2H6) =V(C2H6) / Vm = 10/22.4 = 0.446 mol
2n(C2H6) = 7n(O2)
n(O2) = 7*0.446 / 2 = 1.561 mol
V(O2) = n(O2) * Vm = 1.561 * 22.4 = 35 L
V(возд) = V(O2) * 100% / 21% = 35*100% / 21% = 166.67 L
ответ 166.67 л