Question 6
Helium has just two valence electrons, yet it is as unreactive as neon and argon, which have eight. Why?
The right answer is the one marked above.
Its only shell is already full. The first shell holds a maximum of two electrons, so helium has reached the same condition the others have — a complete outer shell.
Stability comes from a full shell; eight is simply what full means for every shell after the first. Helium does not lose its electrons at all, and like any neutral atom it has equal numbers of protons and electrons.