Correct Option (d):
All the listed devices operate within the 2.4 to 2.5 GHz radio frequency band.
- Bluetooth devices: These devices utilize the 2.4 GHz Industrial, Scientific, and Medical (ISM) band for short-range wireless communication.
- Cordless phones: Many models, particularly older or specific international versions, operate in the 2.4 GHz frequency range.
- Microwave ovens: These appliances function by emitting microwaves at approximately 2.45 GHz to heat food, a frequency that falls within the specified range.
- Wi-Fi devices: Standards such as 802.11b, 802.11g, and 802.11n commonly use the 2.4 GHz band for wireless local area network (WLAN) connectivity.
Incorrect Options:
- Option (a) is incorrect because microwave ovens and Wi-Fi devices also operate within the 2.4-2.5 GHz range.
- Option (b) is incorrect because Bluetooth devices and cordless phones are known to operate in this frequency band.
- Option (c) is incorrect as microwave ovens utilize a frequency of approximately 2.45 GHz for their operation.