Đáp án:

\(\begin{array}{l}
12\,D\\
13\,C\\
14\,\\
a)\,C\\
b)\,A
\end{array}\)

Giải thích các bước giải:

\(\begin{array}{l}
12)\\
{M_{hh}} = 17 \times 2 = 34(g/mol)\\
{n_X} = \dfrac{{6,72}}{{22,4}} = 0,3\,mol\\
 \Rightarrow {m_X} = 34 \times 0,3 = 10,2g\\
hhX:{N_2}(a\,mol),N{O_2}(b\,mol)\\
a + b = 0,3\\
28a + 46b = 10,2\\
 \Rightarrow a = 0,2;b = 0,1\\
13)\\
{M_{hh}} = 19,2 \times 2 = 38,4(g/mol)\\
{n_X} = \dfrac{{9,6}}{{38,4}} = 0,25\,mol\\
hhX:{O_2}(a\,mol),{O_3}(b\,mol)\\
a + b = 0,25\\
32a + 48b = 9,6\\
 \Rightarrow a = 0,15;b = 0,1\\
14)\\
hhY:{O_2}(a\,mol),{N_2}(b\,mol)\\
{n_{hh}} = \dfrac{{5,6}}{{22,4}} = 0,25(mol)\\
a + b = 0,25\\
a:b = 2:3 \Rightarrow 3a - 2b = 0\\
 \Rightarrow a = 0,1;b = 0,15\\
\% {N_2} = \dfrac{{0,15}}{{0,25}} \times 100\%  = 60\% 
\end{array}\)