Answer:
Noun
Step-by-step explanation:
The word attack can be used either as a verb or a noun. When it's a verb, it refers to the action of attempting to cause damage or death to something or someone, and when it is a noun, it refers to an aggressive and violent act or attempt against someone or something.
In the sentence, attack is used as a noun because it is placed after an article: the (Verbs are not placed after an article). Besides, if we replace the word attack for its definition, it makes sense: (...) as the blue alligator closed in for the violent attempt against the purple flamingo.