Final answer:
The word functioning as an adverb is "strangely".
Step-by-step explanation:
In the sentence "The train station was strangely quiet; every step I took echoed off the walls," the word functioning as an adverb is strangely. An adverb modifies a verb, adjective, or another adverb. In this case, "strangely" is describing how the train station was quiet. It gives more information about the quietness.
Learn more about adverbs