Which group of elements has a stable number of electrons in their outer energy level?
a. noble gases
c. halogens
b. alkali metals
d. alkaline earth metals

Which of these statements describes the size of an atom? a. an atom is larger than a sheet of aluminum foil. b. an atom is small but can be seen with just our eyes. c. an atom is the size of a plastic building block. d. an atom is tiny and cannot be seen without magnification.