PTHH :
\(Fe\rightarrow Fe+3e\)
x....................3x
\(Fe\rightarrow Fe+1e\)
y.....................y
\(N+1e\rightarrow N\)
.........0,4......0,4
Giải hệ PT : \(\left\{{}\begin{matrix}56x+72y=12,8\\3x+y=0,4\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=0,1\\y=0,1\end{matrix}\right.\)