Misc: Time ____ when you're having fun?

Questions

What is the only planet that is less dense than water?

What is the only river that flows both north and south of the equator, crossing it twice?

What is the only sport that has a rule against left handed players?

What is the only word in the english language that begins and ends with 'und'?

What is the part of the nose that separates the two nostrils?