9. An unreactive gas. In the comic book world, a mineral containing this element could weaken superman. In the real world, a radioactive form of this element is a by- product of most nuclear explosions: Its presence in the atmosphere can indicate whether a nation is testing nuclear weapons.
10. A reactive metal, with a high melting point. It is used in manufactoring rocket nose cones because this low density substance is remarkably strong.
14. A componet of all living matter and fossil fuels: the black material on a charred candle wick.
10. A reactive metal, with a high melting point. It is used in manufactoring rocket nose cones because this low density substance is remarkably strong.
14. A componet of all living matter and fossil fuels: the black material on a charred candle wick.