Correct Answer: Something that is unknown entirely

Solution : The correct choice will be the third option.

The most appropriate meaning of the idiom up in the air is "something that is uncertain and undecided".

When people say a situation or decision is "up in the air," it means that it is not yet settled or determined, and there is still uncertainty about the outcome. This expression is often used when plans or decisions are pending and not yet finalised, leaving things open-ended or unresolved.