a,
B gồm $H_2$ (x mol), $H_2S$ (y mol)
$n_B=\dfrac{6,72}{22,4}=0,3(mol)$
$\Rightarrow x+y=0,3$ (1)
$\overline{M}_B=11,666.2=23,332$
$\Rightarrow 2x+34y=23,332.0,3=7$ (2)
(1)(2)$\Rightarrow x=0,1; y=0,2$
$\%V_{H_2}=\dfrac{0,1.100}{0,3}=33,33\%\Rightarrow \%V_{H_2S}=66,67\%$
b,
$M+S\buildrel{{t^o}}\over\to MS$
$MS+2HCl\to MCl_2+H_2S$
$M+2HCl\to MCl_2+H_2$
$n_{M\text{dư}}=n_{H_2}=0,1(mol)$
$n_S=n_{M\text{pứ}}=n_{H_2S}=0,2(mol)$
$\Rightarrow 0,2.32+M(0,2+0,1)=25,9$
$\Leftrightarrow M=65(Zn)$