Question

pleasant sound and unpleasant sound

Answer 1

pleasant sound is music unpleasant sound is factory noise
it is dangerous for our ear

Answer 2

The sound which was melodious and low is known as pleasant ex-: Sound of music etc -> Unpleasant sound the sound which have very Much louder voice which can't be hear ex-: Sound of Home theator and etc. Hope it will help u And u know more in Ncert book