$\rm a)$

Thăng bằng electron:

$\begin{array}{c|cc} \rm{\times \;3}&\rm{\mathop{Fe}\limits^{+2}\longrightarrow\mathop{Fe}\limits^{+3}+e}\\\rm {\times\;1}&\rm{\mathop{N}\limits^{+5}+3e\longrightarrow\mathop{N}\limits^{+2}}\\\end{array}$

Cân bằng phương trình:

$\rm 6FeSO_4+  2NaNO_3 +4H_2SO_4\to 3Fe_2(SO_4)_3 +2NO +Na_2SO_4 +4H_2O$

$\rm b)$

Thăng bằng electron:

$\begin{array}{c|cc} \rm{\times \;1}&\rm{2\mathop{Cl}\limits^{+7}+14e\longrightarrow\mathop{Cl_2}\limits^{0}}\\\rm {\times\;7}&\rm{2\mathop{Cl}\limits^{-1}\longrightarrow\mathop{Cl_2}\limits^{ 0}+2e}\\\end{array}$

Cân bằng phương trình:

$\rm KClO_4+8HCl\to 4Cl_2+KCl+4H_2O$