Topic: Interjection,

Best Answer Explained in Below-:

In the sentence "Alas! I am undone," the word "alas" functions as an interjection. Interjections are words or phrases that express strong emotions or sudden bursts of feeling. They are often used to convey a reaction such as surprise, joy, disappointment, or in this case, lamentation or sorrow.

"Alas" specifically communicates a sentiment of regret or concern, signaling that something unfortunate has occurred. This aligns with the nature of interjections, which are typically isolated from the grammatical structure of the surrounding sentence and convey emotional responses directly to the audience.

In contrast, the other options do not fit the function of "alas." A noun represents a person, place, thing, or idea and cannot express emotion in the way "alas" does. An adverb modifies verbs, adjectives, or other adverbs, providing more context about the action, while a preposition shows the relationship between nouns and other words in a sentence. Thus, "alas" does not serve any of these grammatical functions, cementing that its role in this context is indeed that of an interjection.