Answer:
He
Step-by-step explanation:
Helium is a Noble Gas and already has two electrons, or zero valance (zero left). It has achieved a full "outer shell" and doesn't need to gain or lose any electrons by bonding with other atoms. All of the other elements in the list are reactive because they are not noble gasses, and are usually very reactive because they are either a Halogen or an Alkali metal, which only need to gain/lose one electron, which is very little effort, making the atom "try the most" to get that full outer shell for just one electron.