Đáp án đúng: A
Vì $ n=\dfrac{V}{22,4}\to V=22,4.n $ $ \begin{array}{l} {{n}_{{{H}_{2}}}}=\dfrac{{{m}_{{{H}_{2}}}}}{{{M}_{{{H}_{2}}}}}=\dfrac{1}{2}=0,5\,(mol)\to {{V}_{{{H}_{2}}}}={{n}_{{{H}_{2}}}}.22,4=0,5.22,4=11,2\,(l) \\ {{n}_{{{O}_{2}}}}=\dfrac{{{m}_{{{O}_{2}}}}}{{{M}_{{{O}_{2}}}}}=\dfrac{8}{16.2}=0,25\,(mol)\to {{V}_{{{O}_{2}}}}={{n}_{{{O}_{2}}}}.22,4=0,25.22,4=5,6\,(l) \\ {{n}_{{{N}_{2}}}}=\dfrac{{{m}_{{{N}_{2}}}}}{{{M}_{{{N}_{2}}}}}=\dfrac{3,5}{14.2}=0,125\,(mol)\to {{V}_{{{N}_{2}}}}=0,125.22,4=2,8\,(l) \\ {{n}_{C{{O}_{2}}}}=\dfrac{{{m}_{C{{O}_{2}}}}}{{{M}_{C{{O}_{2}}}}}=\dfrac{33}{12+16.2}=0,75\,(mol)\to {{V}_{C{{O}_{2}}}}=0,75.22,4=16,8\,(l) \end{array} $ $ \to $ Thể tích 3,5 gam khí $ {{N}_{2}} $ là thấp nhất.
