Giúp mik với mn helpppppppmeeeee

Em tham khảo nha:

\(\begin{array}{l}
a)\\
{n_P} = \dfrac{{12,4}}{{31}} = 0,4\,mol\\
{n_{{O_2}}} = \dfrac{{20,8}}{{32}} = 0,65\,mol\\
4P + 5{O_2} \xrightarrow{t^0} 2{P_2}{O_5}\\
\dfrac{{{n_P}}}{4} < \dfrac{{{n_{{O_2}}}}}{5} \Rightarrow {O_2} \text{ dư } \\
{n_{{O_2}}} \text{ dư } = 0,65 - 0,4 \times \dfrac{5}{4} = 0,15\,mol\\
b)\\
{n_{{P_2}{O_5}}} = 0,4 \times \dfrac{2}{4} = 0,2\,mol\\
{m_{{P_2}{O_5}}} = 0,2 \times 142 = 28,4g
\end{array}\)