What are bridge elements?

Hint :Bridge elements are those elements which show the diagonal relationship with the element of the neighboring period. Period 2 elements are referred to as bridge elements. For example, $ Be $ is a bridge element as it shows diagonal relationship with $ Al $ .

Complete Step By Step Answer:
Bridge elements are those elements which show the diagonal relationship with the element of neighboring period. Diagonal relationship describes the similarity in certain properties between two elements which placed diagonally when we move from left to right in two neighbouring periods. These properties include comparable atomic size, the polarization of atoms, electronegativity and so on. The elements which show diagonal relationship are illustrated in the following diagram.

Period 2 elements are referred to as bridge elements. These are so called because these elements bridge the gap between metals on one side (group 1 and 2) and nonmetals/metalloids on the other side (group 13-18). Therefore, from the above diagram we conclude that Lithium $ \left( Li \right) $ , beryllium $ \left( Be \right) $ and boron $ \left( B \right) $ are bridge elements.

Additional Information:
Diagonal relationship arises because moving along the period and down the period has opposite effects. For instance, as we move down the group, atomic size increases. In contrast, when we move along the period, atomic size decreases.

Note :
It is important to note that bridge elements are those elements which show the diagonal relationship with the element of the neighboring period. Diagonal relationship describes the similarity in certain properties between two elements which are placed diagonally when we move from left to right in two neighbouring periods. Lithium $ \left( Li \right) $ , beryllium $ \left( Be \right) $ and boron $ \left( B \right) $ are examples of bridge elements.