It receives sound vibration and passes to the eardrum

The correct option is outer ear.

To understand why this is the correct answer, let's look at the structure and function of the ear step-by-step:

1. The Outer Ear: The outer ear consists of the pinna (the visible part of the ear) and the ear canal. The pinna acts like a funnel to collect sound waves from the surrounding environment. These sound waves are guided down the ear canal, where they travel to reach the eardrum (tympanic membrane). Thus, the outer ear is responsible for receiving sound vibrations and passing them to the eardrum.
2. The Eardrum: The eardrum acts as a barrier between the outer ear and the middle ear, vibrating in response to the incoming sound waves.
3. The Middle Ear: Once the eardrum vibrates, it transfers these vibrations to three tiny bones (ossicles) in the middle ear, which amplify the sound.
4. The Inner Ear: The vibrations then reach the cochlea in the inner ear, which translates the physical vibrations into electrical signals for the brain to interpret.
5. The Eustachian Tube: This tube connects the middle ear to the back of the nose and helps equalize air pressure, but it does not direct sound waves to the eardrum.

Therefore, the part of the ear that receives sound vibration and passes it to the eardrum is the outer ear.