Be shows diagonal relationship with-
Na
K
Al
Mg
A diagonal relationship is said to exist between certain pairs of diagonally adjacent elements in the second and third periods (first 20 elements) of the periodic table.
These pairs are (lithium (Li) and magnesium (Mg), beryllium (Be) and aluminum (Al), boron (B) and silicon (Si).
Be shows diagonal relationship with Al. They both have nearly equal electronegativity, small size and availability of only four orbitals in the valence shell. They both form amphoteric oxides and dimeric halides.