Lithium is the most reactive as it is a alkali metal. Helium is the least reactive as it is a Nobel gas with a filled outer valance shell.
Which is the least reactive element? A) C B) H C) Li C) He
C is Carbon, H is Hydrogen, Li is Lithium and He is Helium. I couldn't find a table that included Helium, but out of the others, Lithium is the most reactive and Hydrogen is the least reactive.