Em tham khảo nha :
\(\begin{array}{l}
{n_N} = \dfrac{{4,2}}{{14}} = 0,3mol\\
{n_O} = \dfrac{8}{{16}} = 0,5mol\\
hh:NO(a\,mol),N{O_2}(b\,mol)\\
\left\{ \begin{array}{l}
a + b = 0,3\\
a + 2b = 0,5
\end{array} \right.\\
\Rightarrow a = 0,1;b = 0,2\\
\% {V_{NO}} = \dfrac{{0,1}}{{0,1 + 0,2}} \times 100\% = 33,33\% \\
\% {V_{N{O_2}}} = 100 - 33,33 = 66,67\%
\end{array}\)