Good Riddles

Question: What can float but can't sink.

Question: I stand in one place yet I fill a whole room.
I can be filled with molten rock and come in every hue.

What am I?

Question: At school Joe has three friends: Tim, George and Paige. Two of them play football, two play tennis, and two play golf. The friend who doesn't play golf doesn't play tennis and the one who doesn't play football doesn't play golf. Which sports does each person play?

Question: Which is correct, 9 and 5 is 13 or 9 plus 5 is 13?

Question: Half of those who read this riddle, I am your best friend.
I depend on you, but it's you I will defend.

What am I?