Commercial unit of power.

Kilowatt hour (kWh ) is the commercial unit of power

⇒ 1 kilowatt hour is the energy produced by 1 kilowatt power source in 1 hour 

⇒ 1 kWh = 1kW×1hour=1000×3600W.s

⇒ 1 kWh = 3.6 10⁶ J 

Final Answer:  Hence, the correct option is B, i.e Kilowatt hour