\(a.Mg+HCl\rightarrow MgCl_2+H_2\\ b.n_{Mg}=\dfrac{2,4}{24}=0,1\left(mol\right)\\ n_{MgCl_2}=n_{Mg}=0,1\left(mol\right)\\ \Rightarrow m_{MgCl_2}=0,1.95=9,5\left(g\right)\\ c.n_{H_2}=n_{Mg}=0,1\left(mol\right)\\ \Rightarrow V_{H_2}=0,1.22,4=2,24\left(l\right)\)