What is the difference between Bluetooth and Wi-Fi devices?

The correct answer is A. Bluetooth operates in the unlicensed 2.4 GHz ISM band, using frequency hopping across 79 channels to cope with interference. Wi-Fi (IEEE 802.11) was first standardised for 2.4 GHz, and 802.11a added the 5 GHz band, so Wi-Fi can use either. Since 802.11ax (Wi-Fi 6E), the 6 GHz band is also used, a change after 2011.

• B reverses the roles. Bluetooth is a Personal Area Network (PAN) technology with a range of about 10 metres for most devices, while Wi-Fi is the standard WLAN technology. Neither is a WWAN technology; WWAN refers to cellular networks such as GSM and LTE.
• C is false. Neither technology needs line of sight; both work through walls and obstacles within their range limits.
• D fails because statement B is incorrect.

Core concept: unlicensed ISM bands and short-range wireless networking. For Mains, it links to spectrum management and the problem of many devices sharing the same crowded 2.4 GHz band.

Trap: Aspirants pick B by confusing WLAN with PAN, or pick C from a vague idea that Bluetooth is point-to-point. Check the band and range facts first.