\(a.FeS+2HCl\rightarrow FeCl_2+H_2S\\ b.BTKL:m_{FeS}+m_{HCl}=m_{FeCl_2}+m_{H_2S}\\ \Leftrightarrow20,5+30,5=m_{FeCl_2}+15\\ \Leftrightarrow m_{FeCl_2}=36g\\ c.A_{FeS}=\dfrac{20,5}{88}\cdot6.10^{23}\approx1,4.10^{23}\left(ptử.FeS\right)\\ A_{HCl}=\dfrac{30,5}{36,5}\cdot6.10^{23}\approx5.10^{23}\left(ptử.HCl\right)\\ A_{FeCl_2}=\dfrac{36}{127}\cdot6.10^{23}\approx1,7.10^{23}\left(ptử.FeCl_2\right)\\ A_{H_2S}=\dfrac{15}{34}\cdot6.10^{23}\approx2,65.10^{23}\left(ptử.H_2S\right)\\ d.tỉ.lệ1:2:1:1\)