a) $n_{H_2} = \dfrac{2,479}{24,79} = 0,1(mol)$
$M + 2HCl \to MCl_2 + H_2$
Theo PTHH :
$n_M = n_{H_2} = 0,1(mol) \Rightarrow M = \dfrac{13,7}{0,1} = 137(Bari)$
b) $n_{HCl} = 2n_{H_2} = 0,2(mol) \Rightarrow x = \dfrac{0,2}{0,2} = 1M$
c) $n_{BaCl_2} = n_{H_2} = 0,1(mol)$
$\Rightarrow m_{BaCl_2} = 0,1.208 = 20,8(gam)$