IEEE 802.11 MAC is wifi
(1) True - Max three overlapping channel is possible in wifi
(2) False -RTS (Request to send) and CTS(clear to send) are control frames which is used for collison avoidence not in collison detection
(3) True - Every frame in Wifi is acked, because Wifi station do not use collision detection, in Ethernet we use collision detection, in which it is possible for us to listen channel for collision & use exponential back off in case of collision detection. As in case of wifi, due to more error rate and not using collision detection strategy , we instead use ACK frame, in case of not getting ACK Host will retransmit after Random back off period