|Lighter-than-air party balloons are filled with ____.
|The most malleable and ductile metal element is ____.
|A dense, radioactive, noble gas is ____.
|All ____ atoms have six protons.
|About 78% of the Earth's atmosphere is ____.
|The lightest and most abundant element in the Universe is ____.
|The metal with the highest electrical conductivity is ____.
|A very heavy, stable metal used to shield radiation is ____.