Good Riddles

Question: I'm just a lot of nothing but I'm every were... what am I?

Question: Some friends (5 friends) are climbing an oak tree to get a leaf so who got the pine leaf?

Question: A man wants to start a forest fire.There are 80 trees and you have a lighter. How many trees should he burn?

Question: Which state can you leave or enter without changing your address?

Question: Which city is the dangerous city in the world?