Answer:
Tumultuously in the sentence Now her bosom rose and fell tumultuously is an adverb.
Step-by-step explanation:
Adverbs are words that change or qualify other words, clauses or sentences. Usually, they are used to add further information regarding a verb, an adjective, another adverb, or other clause or sentence, and describe how, where or when an action took place. The most common termination of adverbs is -ly, as in tumultuously, that is providing further information about the verb fell.