Final answer:
Beta waves are typically observed when a person is awake and alert, with the highest frequency of 13–30 Hz and lowest amplitude, indicating full wakefulness and consciousness. The correct option is D.
Step-by-step explanation:
Beta waves are characteristic of a person who is awake and alert. During wakefulness, our brain wave activity is dominated by beta waves, which have the highest frequency ranging from 13–30 Hz and the lowest amplitude compared to other brain waves.
When a person starts to fall asleep, the brain wave activity begins to shift from beta to alpha and then to theta waves as they enter deeper stages of sleep, such as NREM (non-REM) stage 1 sleep, which is associated with alpha waves with a frequency of 8-12 Hz and sleep transitions, and eventually to delta waves in deeper stages of NREM sleep.
Beta waves exhibit the most variability and are distinct from the brain waves observed during the different stages of sleep.