Answer:
The correct sentence that uses "who" and "whom" correctly is:
"Who loves science?"
In this sentence, "who" is used as the subject of the sentence and "loves" is the verb. The question is asking about the subject, so "who" is the correct pronoun to use.
In the other sentences, "whom" is used incorrectly.
In the sentence "The class whom has the best projects will go on a trip," "whom" is used incorrectly as the subject of the verb "has." The correct pronoun to use as the subject is "who," as in "The class who has the best projects will go on a trip."
In the sentence "Jayden is the boy whom scored the goal in the big game," "whom" is used incorrectly as the subject complement. The correct pronoun to use as the subject complement is "who," as in "Jayden is the boy who scored the goal in the big game."
Therefore, the correct sentence that uses "who" and "whom" correctly is "Who loves science?"