I can be seen, I can be not...

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: Look at my face, I am somebody. look at my back, i am nobody. What am I?

Question: What tastes better than it smells?

Question: What goes in the water black and comes out red?

Question: What asks but never answers?

Question: Resurrected, they descend by the millions. Sometimes, to nourish and give life. Other times, to take lives or destroy. They have been known to fill entire valleys and block roads only to disappear before executing their long journey back to the top. What are they?