Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.

$(a)$ Thermal decomposition :

$\underset{Ferrous\,\,sulphate}{\mathop{2FeS{{O}_{4}}}}\,\,\xrightarrow{\Delta }$$\mathop {F{e_2}{O_{3(s)}}}\limits_{Ferric\,\,\,oxide} \, + \mathop {\,S{O_{2(g)}}}\limits_{Sulphur{\text{ }}dioxide\;} \, + \mathop {\,S{O_{3(g)}}}\limits_{Sulphur{\text{ }}trioxide} $

$(b)$ Decomposition by light :

$2AgC{l_{(s)}}\;\xrightarrow{{{\text{ Light }}}}\mathop {2A{g_{(s)}}}\limits_{Silver}  + \mathop {C{l_{2(g)}}}\limits_{Chlorine} $

$(c)$ Decomposition by electricity :

$\mathop {2A{l_2}{O_{3(aq)}}}\limits_{Aluminium{\text{ }}oxide} \xrightarrow{{{\text{ Electricity }}}}\mathop {\;{\kern 1pt} 4A{l_{(s)}}}\limits_{Aluminium}  + \mathop {3{O_{2(g)}}}\limits_{Oxygen} $