What Am I Riddles

Question: To many, I am life's source. I am also its most valuable resource. I create and burn my own precious element, and my destruction will be my punishment. What am I?

Question: Eight of us go fourth, not back, to protect our king from an attack. What are we?

Question: When you say my name, I am no longer there. What am I?

Question: You answer me, but I ask you nothing. What am I?

Question: I am duplicate of you, but only lighter. What am I?