To determine which two elements share the same number of valence electrons, we can refer to the periodic table. Elements are grouped in columns, known as groups, and elements in the same group typically have the same number of valence electrons.
For instance, both sodium (Na) and potassium (K) are in group 1 of the periodic table. This means they each have one valence electron. Similarly, the elements chlorine (Cl) and bromine (Br) are in group 17 and both possess seven valence electrons.
In summary, sodium and potassium each have one valence electron, while chlorine and bromine both have seven. Therefore, there are many pairs of elements that can have the same number of valence electrons based on their group classifications.