What condition is characterized by the hardening of the bony tissue of the middle ear?

The condition characterized by the hardening of the bony tissue of the middle ear is otosclerosis. This condition involves the abnormal growth of bone in the middle ear, which can lead to hearing loss. Specifically, it often affects the stapes bone, one of the three tiny bones (ossicles) in the middle ear responsible for transmitting sound vibrations to the inner ear. When the stapes becomes fixed due to this hardening, it can impede its ability to move freely and effectively transmit sound, resulting in conductive hearing loss.

In contrast, the other options refer to different conditions. Ototoxicity relates to the damaging effects of certain medications on the inner ear and can lead to hearing loss as well, but it does not involve bony tissue. Acoustic neuroma is a benign tumor that affects the vestibulocochlear nerve, leading to hearing and balance issues, but it does not involve hardening of the bones. Ear canal blockage, such as from earwax buildup, can cause temporary hearing loss but does not involve the bony structure of the middle ear. Thus, the defining characteristic of otosclerosis makes it the correct answer for this question.