Question

The opening of nasopharynx, that permits air pressure on both sides of tympanic membrane of the ear to be kept equal, is
A) Oval window
B) Tube of cochlea
C) Auditory nerve
D) Eustachian tube

Answer 1

Hint: Nasopharynx is the upper part of the pharynx which connects the nasal cavity above the soft palate. It is the most superior portion of the pharynx and is externally bounded by skull base and internally by soft palate. Nasopharynx is one among the three sections of the throat.

Complete answer:
Option A) Oval window: The oval window also known as fenestra vestibule. It is the membrane which covers the middle ear from the opening to the cochlea of the inner ear. Its function is to transmit sound to the incus which further passes them to the stapes. Stapes further pushes it to the oval window which sets cochlea fluid in motion.
So, option A is not correct.
Option B) Tube of cochlea: Tube of cochlea is the coiled tube which is divided through most of its length by the inner membranous partition. Due to division in the membrane two fluid filled outer spaces are formed. The function of the cochlea is to transform cochlear liquids sound vibrations into neural signals.
So, option B is not correct.
Option C) Auditory nerve: Auditory nerves are the sensory nerves which transfer auditory information from cochlea to the brain. It is useful for effective hearing. Auditory nerve is also referred to as the acoustic nerve.
So, option C is not correct.
Option D) Eustachian tube: A canal which connects the middle ear to the nasopharynx, that contains the upper throat and back of the nasal cavity. The Eustachian tube maintains air containing space which opens intermittently to equalize the internal air pressure with the air pressure in the external auditory canal.

So Option D is the correct answer.

Note:
Eustachian tube also helps in removing epithelial debris and secretion from the internal ear by ciliary motion and gravity. Any damage to the Eustachian tube may lead to pain and hearing difficulties.