Final answer:
The number of valence electrons is the same for elements within the same group on the periodic table; this similarity accounts for their equivalent chemical properties. Groups are therefore characterized by the same number of valence electrons, influencing their reactivity. Option c.
Step-by-step explanation:
The relationship among the number of valence electrons for each column on the periodic table aligns with choice (c) Groups = same number. Elements within the same group share the same number of valence electrons which define their chemical properties. For instance, alkali metals like lithium and sodium each have one valence electron, while alkaline earth metals such as beryllium and magnesium each have two, and halogens like fluorine and chlorine have seven. This commonality of valence electrons across a group leads to similar chemical behavior, such as how they react by losing, gaining, or sharing electrons.
Furthermore, the elements in a group exhibit similar chemical properties because of their valence shell electron configuration. The vertical columns on the periodic table, referred to as groups or families, showcase elements that behave similarly in chemical reactions due to their shared valence electron arrangement.