Question

What is the antecedent for the pronoun "It" in the following passage?
The sixth-grade students liked volunteering their time to read to the elderly people in the hospital. It made them happy.

Answer 1

Do you know what "antecedent" means?

Answer 2

Well, to begin, we must know what an `antecedent` is.
Definition: "a substantive word, phrase, or clause whose denotation is referred to by a pronoun that typically follows the substantive (such as John in "Mary saw John and called to him") broadly : a word or phrase replaced by a substitute." ~Merriam-Webster

In the example above, `him` is the antecedent for John. John was mentioned previously in the sentence, and they used the word `him` as a substitute.
Since we are looking for the antecedent for the word `it`, look back in the sentence. What was it that made these children happy?