The type of waves on EEG seen in Stage- IV NREM sleep is

(D) 8 (Delta) > There are two different kinds of sleep: rapid eye movement (REM) sleep and non-REM (NREM), or slow-wave sleep.> NREM sleep is divided into four stages. A person falling asleep first enters stage 1, which is characterized by low-amplitude, nigh- frequency EEG activity. Stage 2 is marked by the appearance of sleep spindles. These are bursts of alpha-like, 10-14 Hz, 50 uV waves.> In stage 3, the pattern is one of lower frequency and increased amplitude of the EEG waves. Maximum slowing with large waves is seen in stage 4. Thus, the characteristic of deep sleep is a pattern of rhythmic slow waves, indicating marked synchronization.