Li shows diagonal relationship with:
(A) Mg
(B) Be
(C) Al
(D) B

Hint: Diagonal relationship is observed between pairs of diagonally adjacent elements present in the second and third period of the periodic table. Out of the elements magnesium, beryllium, aluminum and boron, identify the element that is present diagonally adjacent to lithium.

Complete answer:
Lithium, beryllium and boron are present in the second period of the periodic table. Magnesium and aluminum are present in the third period of the periodic table.




In the second and third period of the periodic table, there are certain pairs of diagonally adjacent elements that show diagonal relationship. These pairs of diagonally adjacent elements, shows some similarity in the properties. The extent of these similarities in the properties is much lower than the similarities within a group. These similarities in the properties of diagonally adjacent elements are due to the similar polarizing power, similar ionic charge to size ratio of diagonally adjacent elements.
Second period metals that are present in groups 1, 2 and 13, show diagonal relationship. Lithium shows diagonal relationship with magnesium. Beryllium shows diagonal relationship with aluminum. Boron shows diagonal relationship with silicon.

Hence, the correct answer is the option (A).

Note: Lithium and magnesium have similar polarization power. On heating with air or oxygen, both lithium and magnesium form monoxide. Thus, due to diagonal relationship, both lithium and magnesium show similar properties.