Which of the given wireless technologies used in IoT, consumes the least amount of power?

Explanation

Zigbee, built on IEEE 802.15.4, was designed specifically for low-rate, low-duty-cycle sensor networks; its nodes sleep most of the time and typically draw on the order of tens of milliwatts, letting battery-powered devices run for years. Classic Bluetooth consumes noticeably more, Wi-Fi far more again because of its higher data rate and constant association overhead, and cellular GSM/CDMA radios are the most power-hungry of the four because of their transmit power and network signalling. So Zigbee is the lowest-power option here.