<prompt> Arousal is most difficult in which stage of sleep -Stage 1 NREMStage 2 NREMStage 3,4 NREMREM  <response>: Ans is c i.e., Stage 3,4 NREMIn general, the ease of arousal from sleep parallels the ordering of the sleep stages, with NEM and stage 1 being the easiest for arousal and stage 4 the most difficult. 