Commercial unit of electrical energy is _______.
(A) \[\text{joule}\]
(B) \[\text{joule/second}\]
(C) \[\text{watt}\]
(D) \[\text{kilowatt-hour}\]

Hint: Electrical Energy is the ability of a circuit to produce work by creating an electrical action. The action of the circuit can manifest in many forms, such as thermal, electromagnetic, mechanical, electrical, etc. Electrical energy can be created from batteries, generators, dynamos, photovoltaics, etc. Energy is stored for future use using fuel cells, batteries, capacitors or magnetic fields, etc.

Complete solution:
The commercial unit of electricity is \[\text{kilowatt-hour}\] . The electric energy or power consumed in factories, industries and houses, is measured in \[\text{kilowatt-hour}\] . The \[\text{kilowatt-hour}\] (SI symbol commonly written as kWh) is a unit of energy equal to \[3600{\text{kilojoules}}\] (\[3.6{\text{megajoules}}\]). The \[{\text{kilowatt-hour}}\] is commonly used as a billing unit for energy delivered to consumers by electric utilities. If you know what a \[{\text{kilowatt-hour}}\] is, it can help you understand:
How your commercial energy provider decides your electricity consumption and bill
Why some electrical devices consume much more electricity than others. We can also work out the individual power and energy consumption by each appliance.
The importance of turning appliances off to save energy consumption.
Hence, we can say that the commercial unit of electrical energy is \[{\text{kilowatt-hour}}\].

Option (D) is the correct answer to our given question.

Note: There is often a confusion between \[{\text{kilowatt}}\] and \[{\text{kilowatt-hour}}\]. A \[{\text{kilowatt}}\] is simply \[1,000\text{ watt}\] , which is a measure of power. So, for example, the \[10,000\text{ watt}\] electric shower could also be called a \[10{\text{kilowatt}}\] shower. A \[{\text{kilowatt-hour}}\] (kWh) is a measure of energy. So a \[1000\text{ watt}\] drill needs \[1000\text{ watt}\] of power to make it work, and uses \[1kWh\] of energy in an hour.