Two of most unique elements on the periodic table are hydrogen and helium. What makes them so unique and removed from the other groups on the periodic table?

a
Unlike all other elements, hydrogen and helium are gases
b
Unlike all other elements, hydrogen and helium are not considered metals
c
Unlike all other elements, hydrogen and helium only have a maximum of 2 valence electrons
d
Unlike all other elements, hydrogen and helium have very limited properties