I think 터져요 should also be accepted.
The formalities being different shouldn't result in incorrect answers .
Why is 터지다 wrong..just because it's not high formal?
Many of the sentences are missing valid translations, so please submit reports and they'll be added. Here, though, 터지다 might not be accepted because it is the infinitive form and not conjugated for normal use in a sentence
터집니다 is wrong because you don't use high formalities for anything that isn't a person other than yourself. Since it's an inanimate object, you don't need to show any respect to it
explode is more like 폭발