Consider the following : 1. Bluetooth device 2. Cordless phone 3. Microwave oven 4. Wi-Fi device Which of the above can operate between 2-4 and 2-5 GHz range of radio frequency band ?

All four device types operate in or commonly use the 2.4–2.5 GHz ISM region. Bluetooth is specified to operate in the globally available 2.4 GHz ISM band [1]. Wi‑Fi standards (802.11b/g/n) also utilize the 2.4 GHz band, sharing spectrum with other consumer devices. Microwave ovens typically use a magnetron near 2.45 GHz, which lies within this ISM band and is a common source of interference to other 2.4 GHz equipment. Cordless telephones have historically included models that operate in the 2.4 GHz range and are listed among common 2.4 GHz interferers alongside Wi‑Fi, Bluetooth and microwaves. Therefore, options 1, 2, 3 and 4 are all correct.

Sources

1. [1] https://www.sciencedirect.com/topics/computer-science/bluetooth-device