Which clause in this sentence is restrictive?

[One student asked,] ["Why are we going] [to see a movie] [that's an animated cartoon] [for our science class?"]

That's an animated cartoon

[that's an animated cartoon]

Explanation:

A restrictive clause refers to an adjective clause that essentially modifies the noun that comes before it in a sentence. A restrictive clause is necessary in a sentence for it to have a meaning because it puts a limitation on the thing it is making reference to in the sentence, Therefore, if a restrictive clause is removed from the sentence, the meaning of the sentence will change.

Relative pronouns who, whose, whom, or that is used to introduce restrictive clause in a sentence.

In the question, [that's an animated cartoon] is a restrictive clause which is introduced into the sentence by the relative pronoun "that". It modifies "a movie" which is the noun that preceded it by putting a limit on the noun. The meaning of the sentence will therefore change if [that's an animated cartoon] is removed from the sentence.