Final answer:
The synonym for sonorous is (d) 'Sonority,' relating to a deep, rich, and resonant sound. 'Intensity level or decibel' describes the loudness of sound.
Step-by-step explanation:
Sonorous refers to a sound that is deep, rich, and resonant, often having a powerful, imposing tone. While 'sonorant' is related, it typically refers to a class of sounds, not the quality of sound itself. 'Sonoriferous' and 'sonoriferously' are not commonly used and do not precisely align as synonyms for sonorous.
The answer to the question about loudness of sound in reference to the list provided is b. intensity level or decibel. This is because intensity level and decibels measure the power of sound waves, which is directly related to how loud a sound is perceived.