\[\begin{array}{l}
Fe + 2HCl \to FeC{l_2} + {H_2} \uparrow \\
a \to 2a \to a \to a\\
FeS + 2HCl \to FeC{l_2} + {H_2}S \uparrow \\
b \to 2b \to b \to b\\
a + b = \dfrac{{6,72}}{{22,4}} = 0,3\left( {mol} \right)\\
{H_2} + Pb{\left( {N{O_3}} \right)_2}\xcancel{ \to }\\
Pb{\left( {N{O_3}} \right)_2} + {H_2}S \to PbS + 2HN{O_3}\\
\;\,\;{\kern 1pt} \;\;\;\;\;\;\;0,2 \leftarrow 0,2 \leftarrow 0,2 \to 0,4\\
{n_{PbS}} = \dfrac{{47,8}}{{207 + 32}} = 0,2\left( {mol} \right) \Rightarrow {n_{{H_2}S}} = 0,2\left( {mol} \right) \Rightarrow {n_{{H_2}}} = 0,1\;mol\\
{n_{Fe}} = {n_{{H_2}}} = 0,1mol,{n_{FeS}} = 0,2mol\\
\% {m_{Fe}} = \dfrac{{{m_{Fe}}}}{{{m_{Fe}} + {m_{FeS}}}}.100\% = \dfrac{{0,1.56}}{{0,1.56 + 0,2.\left( {56 + 32} \right)}}.100\% = 24,1\% \\
\% {m_{FeS}} = 100\% - 24,1\% = 75,9\%
\end{array}\]
