$1)$

Chất khử: $Al$

Chất Oxy-hóa: $H_2SO_4(đặc)$

$\text{ x 2 | }$$\mathop{Al}\limits^{0} \to \mathop{Al}\limits^{+3}+3e $

$\text{ x 3 | }$$\mathop{S}\limits^{+6}+2e \to \mathop{S}\limits^{+4} $

`->`$2Al+6H_2SO_4 (đặc) \xrightarrow{t^o} Al_2(SO_4)_3+3SO_2+H_2O$

$2)$

Chất khử: $H_2S$

Chất Oxy-hóa: $SO_2$

$\text{ x 2 | }$$\mathop{S}\limits^{-2} \to \mathop{S}\limits^{0}+2e $

$\text{ x 1 | }$$\mathop{S}\limits^{+4}+4e \to \mathop{S}\limits^{0} $

`->`$2H_2S+SO_2 \xrightarrow{t^o} 3S+2H_2O $

$3)$

Chất khử: $HCl$

Chất Oxy-hóa: $MnO_2$

$\text{ x 1 | }$$\mathop{2Cl}\limits^{-1} \to \mathop{Cl_2}\limits^{0}+2e $

$\text{ x 1 | }$$\mathop{Mn}\limits^{+4}+2e \to \mathop{Mn}\limits^{+2} $

`->`$MnO_2+4HCl \to Cl_2+MnCl_2+2H_2O $

$4)$

Chất khử: $H_2S$

Chất Oxy-hóa: $O_2$

$\text{ x 2 | }$$\mathop{S}\limits^{-2} \to \mathop{S}\limits^{+4}+6e $

$\text{ x 3 | }$$\mathop{O_2}\limits^{0}+4e \to \mathop{2O}\limits^{-2} $

`->`$2H_2S+3O_2 \xrightarrow{t^o} 2SO_2+2H_2O $

`a)`

Chất khử: `Al`

Chất oxh: `H_2SO_4`

`Al->Al^{+3}+3e|xx2`

`S^{+6}+2e->S^{+4}|xx3`

`2Al+6H_2SO_4->Al_2(SO_4)_3+3SO_2+6H_2O`

`b)`

Chất khử: `H_2S`

Chất oxh: `SO_2`

`S^{-2}->S+2e|xx2`

`S^{+4}+4e->S|xx1`

`2H_2S+SO_2->3S+2H_2O`

`c)`

Chất khử: `HCl`

Chất oxh: `MnO_2`

`2Cl^{-}->Cl_2^0+2e|xx1`

`Mn^{+4}+2e->Mn^{+2}|xx1`

`MnO_2+4HCl->MnCl_2+Cl_2+2H_2O`

`d)`

Chất khử: `H_2S`

Chất oxh: `O_2`

`S^{-2}->S^{+4}+6e|xx2`

`O_2^0+4e->2O^{-2}|xx3`

`2H_2S+3O_2` $\xrightarrow{t^o}$ `2SO_2+2H_2O`