The correct answer is:
c) Unlike all other elements, hydrogen and helium only have a maximum of 2 valence electrons.
Hydrogen has one electron in its outer shell (which is also its only shell) and can hold a maximum of 2 electrons when it forms bonds. Helium has two electrons in its outer shell and is stable because it fills its shell (1s²), making it a noble gas. This characteristic of having a maximum of 2 valence electrons sets them apart from most other elements in the periodic table, which typically have more than 2 valence electrons.
While answer (b) contains a true statement—that both hydrogen and helium are not metals—it does not capture the unique aspect of their electronic configuration.