What part of speech is represented by the word in parentheses: Jack is (critically) ill.

In the sentence "Jack is (critically) ill," the word "critically" functions as an adverb. Adverbs typically modify verbs, adjectives, or other adverbs, providing additional information about how an action is performed or the degree of a quality. In this case, "critically" modifies the adjective "ill," specifying the extent of Jack's illness.

When considering the other parts of speech, a noun represents a person, place, thing, or idea; an adjective describes or modifies a noun; and a verb conveys action or a state of being. In this context, "ill" is an adjective describing Jack's state, while "critically" enhances that description, indicating how serious or severe the condition is. Thus, recognizing "critically" as an adverb is essential in understanding its role in conveying the severity of Jack's illness.