What characteristic of helium distinguishes helium from the other noble gases?

The characteristic that helium has that distinguishes it from the noble gases would be that it only has 2 valence electrons while noble gases has a completely filled orbitals giving it 8 valence electrons and a stable electron configuration. The valence electrons is the number of electrons that is present in an atom that can take part in the formation of bonds. These electrons can be found on the outermost shell of an atom. Helium is an exception to the octet rule, its atom has only two available electrons in its outermost shell since it only has one eletron shell that is the only the s orbital which can hold two electrons only. 

The  grandmother cell  is a hypothetical  neuronthat represents a complex but specific concept or object.[1]  it activates when a person "sees, hears, or otherwise sensibly discriminates"[2]  a specific entity, such as his or her grandmother. the term was in use at least as early as 1966 amongst staff and students in the department of experimental psychology, university of cambridge, england. a similar concept, that of the  gnostic neuron, was proposed two years later

Reaction type : double replacement hcl + lioh = h2o + licl