Final answer:
The top receptacle of a duplex outlet is often the switched receptacle to allow for a lamp to be controlled by a wall switch, while keeping the bottom receptacle powered for continuous use. However, this is not a fixed rule and may vary.
Step-by-step explanation:
The statement regarding a duplex receptacle is generally true. In many residential and office buildings, the top receptacle of a duplex outlet is often wired to be the switched receptacle. This setup allows for a lamp or other device to be turned on and off using a wall switch, while the bottom receptacle remains constantly powered for other devices. However, the actual configuration can vary depending on the wiring choices made by the electrician or the building codes in your area. There is no strict rule that it has to be the top receptacle; it is simply a common practice for convenience and standardization.