For the IEEE 802.11 MAC protocol for wireless communication, which of the following statements is/are TRUE? I. At least three non-overlapping channels are available for transmissions. II. The RTS-CTS mechanism is used for collision detection. III. Unicast frames are ACKed.

Let us analyze each statement for the IEEE 802.11 MAC protocol:

1. Statement I is TRUE: In the standard 2.4 GHz ISM band used by IEEE 802.11b/g/n, there are at least three non-overlapping channels (channels 1, 6, and 11). In the 5 GHz band (802.11a/n/ac/ax), even more non-overlapping channels are available.

2. Statement II is FALSE: In wireless transmission, collision detection is impractical because a transmitting station's own signal overwhelms any incoming signal. Hence, IEEE 802.11 uses CSMA/CA (Collision Avoidance). The RTS/CTS (Request to Send / Clear to Send) mechanism is used for collision avoidance and solving the hidden terminal problem, not for collision detection.

3. Statement III is TRUE: Since wireless media are prone to errors and stations cannot detect collisions during transmission, IEEE 802.11 requires every successfully received unicast frame to be acknowledged with an explicit ACK frame.

Therefore, only statements I and III are true, corresponding to option (B).