Concept:Beryllium and aluminium show a diagonal relationship in the periodic table.Explanation:Beryllium is in Group 2, Period 2, while aluminium is in Group 13, Period 3.They are positioned diagonally to each other, and diagonal elements often have similar properties because their charge-to-radius ratios are comparable.This explains the similarity in their chemical behaviour, such as forming amphoteric oxides and covalent compounds.Answer:D. are positioned diagonally to each other