EEG taken during which of the following sleep stages shows sleep spindles?

Stage 2 sleep, a component of Non REM sleep is characterised by the presence of sleep spindles and K complexes. Sleep spindles appears as sinusoidal waves occurring at a frequency of 12-14 Hz. K complexes are occasional high voltage biphasic waves. Stage 1 sleep is characterised by the presence of theta waves 4-Hz). In stage 3 of NREM sleep, a high-amplitude delta rhythm (0.5-4 Hz) are seen. Stage 4 of NREM sleep is characterised by the presence of slow waves. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 14. Electrical Activity of the Brain, Sleep--Wake States, & Circadian Rhythms. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.