Be shows the diagonal relationship with

The correct answer/option is Al (Aluminum).

Understanding Diagonal Relationships:
In the periodic table, a diagonal relationship exists between certain elements of the second and third periods that are placed diagonally adjacent to each other. This relationship arises because of the similarity in their ionic sizes and electronegativity values. As we move across a period (from left to right), the size of atoms/ions decreases and electronegativity increases. Conversely, as we move down a group, the size increases and electronegativity decreases. When we move diagonally (down and to the right), these two opposing trends partially cancel each other out, resulting in similar chemical properties.

Comparing Beryllium (Be) and Aluminum (Al):
Beryllium (Be) belongs to Group 2 and Period 2 of the periodic table, while Aluminum (Al) belongs to Group 13 and Period 3.
Be is diagonally adjacent to Al in the periodic table:
Group 2: Be
Group 13: (B) → Al (diagonally down from Be)

Due to this diagonal relationship, Beryllium (Be) and Aluminum (Al) share several similar characteristics:
1. Both elements form oxides ($\mathrm{BeO}$ and ${\mathrm{Al}}_2{O}_3$) that are amphoteric in nature, meaning they react with both acids and bases.
2. Both form covalent halides (like ${\mathrm{BeCl}}_2$ and ${\mathrm{AlCl}}_3$) which act as Lewis acids and are soluble in organic solvents.
3. Both metals resist the action of concentrated nitric acid (${\mathrm{HNO}}_3$) due to the formation of a protective passive oxide film on their surfaces.