Diagonal relationship is shown by:A.Elements of first periodB.Elements of second periodC.Elements of third periodD.Elements of fourth period

Diagonal relationships in chemistry typically refer to similarities in properties and behavior between elements in different periods of the periodic table that are diagonally positioned from each other. These diagonal relationships are most commonly observed between elements in the second and third periods and between elements in the third and fourth periods.

So, the correct answer to your question is:

C. Elements of the third period

Diagonal relationships are often seen between elements in the second and third periods, such as lithium (Li) and magnesium (Mg), and between elements in the third and fourth periods, such as boron (B) and silicon (Si). These elements share certain similarities in properties due to their diagonal positioning in the periodic table.