Question

Theoretically, which nonmetal should be the most reactive?

He
Rn
F
At

Answer 1

He and Rn are noble gases as their valence shells are full. So they are the least reactive.Astatine has a lower En and Ea than Flourine (being the most electronegative element). Thus pushes Flourine to be the most reactive

Answer 2

Also, with At, the principle quantum number is greater. This means lower Coulombic FOAs, and greater nuclear shiedling and electron-electron repulsion. The P+:e- ratio is less than flourine's though they're both halogens. So that makes At even less reactive.