nFe = a (mol)
nAl = b (mol)
=> 56a + 27b = 8.3 (1)
nH2 = PV/RT = 8.4*1 / 0.082 * (136.5 + 273) = 0.25 (mol)
Fe + 2HCl => FeCl2 + H2
2Al + 6HCl => 2AlCl3 + 3H2
nH2 = a + 1.5b = 0.25 (mol) (2)
(1) , (2) :
a = b = 0.1
%Fe = 0.1*56/8.3 * 100% = 67.47%
%Al = 32.53%