In which sentence is "that" used incorrectly? The butterfly that was eaten by the bird was poisonous. The letter that was opened in the hall was not for me. The song that played on the radio reminded me of my childhood. The student that won the spelling bee received a $50 gift card to the bookstore.

I believe the sentence in which "that" was used incorrectly to be:

The student that won the spelling bee received a $50 gift card to the bookstore.

Explanation:

First, we need to understand that the relative pronoun "that" can be used to refer to people, animals, and things. However, when it comes to formal English, it is best to avoid it when referring to people. When doing so, the best choice is to replace it with either "who" or "whom", according to the necessity. Specially when writing, since writing tends to be formal, using "that" for people can be seen as uncouth. Having that in mind, the option that uses "that" incorrectly, according to formal standards, is: The student that won the spelling bee received a $50 gift card to the bookstore. The best way to correct is is: The student who won the spelling bee received a $50 gift card to the bookstore.

the correct answer is the first one.