Diagonally related elements in the periodic table are called as:

• A. Triads
• B. Representative elements
• C. Lanthanide series
• D. Bridge elements

Answer: (D)

Bridge elements describe diagonally related elements in the periodic table. This diagonal relationship shows up when you move one group to the right and one period down, producing pairs with surprisingly similar chemical behavior despite being in different blocks. The reason is that going down a period increases size and shielding, while moving to the right increases effective nuclear charge, and moving diagonally tends to balance these effects. As a result, the cations these elements form have similar charge densities and polarizing power, which leads to comparable bonding character and oxide/hydride chemistry. That’s why Li–Mg, Be–Al, and B–Si pairs exhibit parallel properties, so these elements are described as bridge elements. Other terms like triads, representative elements, or the lanthanide series refer to different groupings or concepts in the periodic table, not the diagonal, bridging relationship.