Good Riddles

Question: I always listen to my Master, I never disobey. From my path I never stray to destroy what's in my way. What am I?

Question: What lightens the light and darkens the dark?

Question: How much is a good night sleep worth?

Question: what is yours but you can't actually hold ?

Question: Tommy is in a cave. He stops to find two tunnels. There is a guard before each tunnel. Tommy knows two things: 1. One tunnel leads to the fields of punishment and the other fields of rewards 2. One guard always lies and the other always tells the truth. Tommy can only ask one yes or no question to either one of the guards. The tunnels and guards look exactly the same. What question can Tommy ask to get to the fields of rewards and not death?