\(a)MgCl_2 + 2NaOH \to Mg(OH)_2 + 2NaCl\\ Mg(OH)_2 \xrightarrow{t^o} MgO + H_2O\\ b) n_{MgO} = n_{Mg(OH)_2} = n_{MgCl_2} = \dfrac{19}{95} = 0,2(mol)\\ \Rightarrow m = 0,2.40 = 8(gam)\\ c)n_{NaCl} = 2n_{MgCl_2} = 0,2.2 = 0,4(mol)\\ m_{NaCl} = 0,4.58,5 = 23,4(gam)\)