Concept:Elements in the same group of the periodic table have identical outer-shell electron arrangements.
Explanation:The periodic table arranges elements in vertical columns called groups.
All elements in a group have the same number of valence electrons, which are the electrons in the outermost shell.
These valence electrons largely determine the chemical properties of the elements.
The number of neutrons, the number of isotopes, and the atomic number are not the same for elements within a group.
Hence, the property shared by elements in the same group is their number of valence electrons.
Answer:B. number of valence electrons