Good Riddles

Question: What is it you like to kill, but actually kills you?

Question: You see us everyday, but you never see us together. We appear everywhere but never are we together at the same place. Who are we?

Question: I can be seen, I can be not. Thanks to me, you'll fall in love. I mostly am sweet, but once I were sour. You can receive me, you can't just buy me. You only can send me, or simply share me. What Could I be?

Question: Before man discovered Mt. Everest, what was the tallest mountain in the world?

Question: A pond with dimension of 6m by 3m wil be filled of water lilies at exactly 30 days. Each day the number of water lilies will be doubled. First day 1, second day 2 etc... On what day it will fill half of the pond?