Tiếp 
TH2:
M tác dụng vs HCl
Mg+ 2HCl-----------> MgCl2+ H2
a_______________________a
2M+ 2nHCl----------> 2MCln+ nH2
b_______________________bn/2
2M+2m H2SO4----------> M2(SO4)m+ mSO2+ 2mH2O
b______________________________bm/2
Mg+ 2H2SO4----------> MgSO4+ SO2+ 2H2O
a__________________________a
nH2 =a+bn/2 =0,4 mol
=> 24a+ 12bn = 9,6g
nSO2 =a+bm/2 =0,5 mol
=> 24a + 12bm= 12 g
mhh = 16g
=> 24a+ bM = 16
=> bM - bm= 4
=> bM-bn =6,4 g
=> (M-m)/(M-n) =4/6,4=5/8
=> M= 32m -20 n
biện luận => m=3
n=2 
M=56 => M là Fe