Answer: The diagonal relationship is present between the lighter elements of periods second, thirds.
Explanation:
Elements which are present diagonally adjacent to each other in the second and third periods of the periodic table tends to show diagonal relationship as they have similar properties.
For example, Lithium is a second period element and magnesium is a third period element.
Hence, lithium and magnesium show diagonal relationship with each other.
Thus, we can conclude that diagonal relationship is present between the lighter elements of periods second, thirds.
