What element is 78% of earth's atmosphere made of?

One of the following properties was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version. which property fits this description?

Flourine is found to undergo 10% radioactivity decay in 366 minutes determine its halflife

The peak wavelength for the blackbody curve of a star is in the uv range. assuming the radiation from this star can reach earth, would you be able to see it?