Final answer:
The frequency most likely to be coded closest to the apex of the cochlea is 300 Hz, as lower frequency sounds are coded at the apex, while higher frequency sounds are coded at the base of the cochlea.
Step-by-step explanation:
The frequency that is likely to be coded closest to the apex of the cochlea is 300 Hz. The cochlea encodes auditory stimuli for frequencies between 20 Hz and 20,000 Hz, where lower frequencies are detected by hair cells at the apex of the cochlea, and higher frequencies are encoded by hair cells at the base of the cochlea. Therefore, of the options provided (15,000 Hz, 18,000 Hz, 300 Hz, 1,000 Hz), 300 Hz is the frequency that would be coded closest to the apex of the cochlea. The human hearing range typically extends from 20 Hz to 20,000 Hz, with the threshold of hearing in decibels varying depending on the specific frequency.