$n_{N_2} = a(mol) ; n_{O_2} = b(mol)$
Coi $n_X = 1(mol) \Rightarrow a + b = 1(1)$
Ta có : $M_X = \dfrac{28a + 32b}{a + b} = 14,5.2(2)$
Từ (1)(2) suy ra : a = 0,75 ; b = 0,25
$\%m_{N_2} = \dfrac{0,75.28}{0,75.28 + 0,25.32}.100\% = 72,4\%$
$\%m_{O_2} = 100\% - 72,4\% = 27,6\%$
$\%V_{N_2} = \dfrac{0,75}{1}.100\% = 75\%$
$\%V_{O_2} = 100\% - 75\% = 25\%$