Question

equation for decomposition reaction where energy is supplied in the form of heat light or electricity

Answer 1

2FeSO4--heated---- Fe2O3+SO2+SO3 This is when heating 2AgCl-------- 2Ag+Cl2 This is in presence of light These are few examples of decomposition  

Answer 2

Heat:
CaCO3 on heating gives CaO+CO2
Electricity:
H2O on electrolysis gives H2+ O2
Light:
This equations are used in black and white photography

AgCl gives Ag + Cl2

AgBr gives Ag + Br2