There is a type of liquid i read about in a book:

Mixed with certain substances it becomes a lethal poisen, and mixed with others it can become an incredibly corrosive acid. And yet millions of people die from lack of it each year.

What is it?

Dihydrogen Monoxide:

H20

Water

And wat about this:

Pure chlorine was used in WWII as a lethal gas, and killed millions of people. Pure sodium is an acid corresive enough to eat through steel. And when you combine them together you get...

Sodium chloride:

Table salt

And finally:

The is a type of volcano known as a supervolcano, basically one that is massive (duh). There is only one active one, underneath a national park in America. If it exploded it would bury America in around 10m of ash and block out the sun for years. Scary huh?

And another thing: It is supposed to erupt about once every 6 million years. And it erupted 6 million years ago.