PTHH: \(R+2HCl\rightarrow RCl_2+H_2\)
Ta có: \(n_{HCl}=0,4\cdot3=1,2\left(mol\right)\) \(\Rightarrow n_R=0,6mol\)
\(\Rightarrow M_R=\frac{14,4}{0,6}=24\left(đvC\right)\) \(\Rightarrow\) R là Magie
Theo PTHH: \(n_{MgCl_2}=n_{Mg}=0,6mol\)
\(\Rightarrow C_{M_{MgCl_2}}=\frac{0,6}{0,4}=1,5\left(M\right)\)