Option (3) is correct because organ of Corti is located on the Basilar membrane, thus (a) in column-I matches with (iv) in column-II. The coiled portion of the labyrinth is called cochlea, so (b) matches with (ii) in column II. The eustachian tube connects the middle ear cavity with the pharynx, thus (c) matches with (i) in column-II. The middle ear contains ossicle called Stapes that is attached to the oval window of the cochlea, so (d) matches with (iii) in column II.