Good Riddles

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: What can float but can't sink.

Question: Two men are facing each other alone in a large room. There is a clock on the wall. One man, who thinks of himself as a prophet, says to the other, "In five minutes you'll be stabbed in the back."

The other man is very distraught and stares at the clock. After five minutes he is stabbed in the back.

What happened?

Question: 4 people fall out of a boat and only 3 get their hair wet.

Question: When the clock has no angle I will own yesterday, tomorrow and tonight What m I?