What Am I Riddles

Question: I'm number three.
But I'm not a number.
I'm hot and cold at the same moment but not at the same time.
I'm number three.
But I'm not a number.

Who or what am I?

Question: I am apart of everything, including you. Once I die, I will begin anew. As my life status becomes dire, I burn brighter and brighter. What am I?

Question: What has classes but moves?

Question: Many have heard me, but nobody has seen me, and I will not speak back until spoken to.What am I?

Question: Smell me, buy me, and deliver me.
I won't change.

What am I?