Concept:Beryllium and aluminum illustrate the diagonal relationship in the Periodic Table.
Explanation:Beryllium is located in Group 2 and Period 2.
Aluminum is located in Group 13 and Period 3.
They do not belong to the same group or the same period.
Instead, they are positioned diagonally to each other.
This diagonal placement makes their charge density and polarizing power similar.
As a result, beryllium behaves like aluminum in many chemical properties.
For example, both form covalent compounds and react with alkalis.
Answer:D. are positioned diagonally to each other.