$\color{red}{\text{Lyy}}$

Gọi khối lượng khí nitrogen và hydrogen là `m (g)` (vì cùng khối lượng).

`⇒` $n_{N_2}$ `=` $\dfrac{m}{28}$ (`mol`).

      $n_{H_2}$ `=` $\dfrac{m}{2}$ (`mol`).

$M_{hh}$ `=` $\dfrac{m + m}{n_{N_2} + n_{H_2}}$ `=` $\dfrac{2m}{\dfrac{m}{28} + \dfrac{m}{2}}$

              `=` $\dfrac{2m}{m(\dfrac{1}{28} + \dfrac{14}{28})}$ `=` $\dfrac{2}{\dfrac{15}{28}}$

              `=` $\dfrac{56}{15}$ (`g`/`mol`)

`⇒` $d_{hh}/O_2$ `=` $\dfrac{M_{hh}}{M_{O_2}}$ `=` $\dfrac{\dfrac{56}{15}}{32}$ `=` $\dfrac{7}{60}$ $\approx$ `0,117`.