Explanation:

The idiom "an elephant in the room" refers to an obvious, significant problem or difficult subject that everyone present is aware of but deliberately avoids discussing due to discomfort or embarrassment. Option (1) accurately captures this meaning. Option (2) is incorrect as the idiom is not about physical accommodation. Option (3) is partially correct in that it's a big issue, but it misses the crucial aspect of deliberate avoidance. Option (4) is incorrect; the issue is indeed avoided by not talking about it, which is the core of the idiom.