$2KNO_3\rightarrow 2KNO_2+O_2$ $x x 0,5x$
$2Zn(NO_3)_2\rightarrow 2ZnO+4NO_2+O_2$
$y y 2y 0,5y$
$2Cu(NO_3)_2\rightarrow 2CuO+4NO_2+O_2$
$z z 2z 0,5z$
$8Fe(OH)_2+26HNO_3\rightarrow 8Fe(NO_3)_3+N_2O+21H_2O$
$0,064 \rightarrow 0,008$
$\Rightarrow n_{B}=n_{N_2O}=0,008 mol\Rightarrow 0,5x+2,5y+2,5z=0,008 (1)$
$d_{B/H_2}=19,5\Rightarrow \frac{46(2y+2z)+32(0,5x+0,5y+0,5z)}{(2y+2z)+(0,5x+0,5y+0,5z)}=2.19,5$
$\Rightarrow 2y+2z=0,5x+0,5y+0,5z\Rightarrow x=3(y+z) (2)$
Mặt khác:
$\frac{85x+81y+80z}{101x+189y+188z}=\frac{671}{983} (3)$
$\Rightarrow \begin{cases}(1) \\(2)\\(3) \end{cases}\Rightarrow \begin{cases}x=... \\ y=...\\z=... \end{cases}$