Which elements of group $1$ and $2$ differ from the other elements of the same group? Give a brief explanation of the diagonal relationship.

(N/A) Lithium $(Li)$ and beryllium $(Be)$,the first elements of Group $1$ and Group $2$ respectively,exhibit anomalous properties that differ from the other members of their respective groups.
In these anomalous properties,they resemble the second element of the following group. Thus,lithium shows similarities to magnesium $(Mg)$ and beryllium shows similarities to aluminium $(Al)$ in many of their properties.
This type of diagonal similarity is referred to as the diagonal relationship in the periodic table. The diagonal relationship arises due to the similarity in ionic sizes and/or the charge/radius ratio $(ionic \ potential)$ of the elements.
Monovalent sodium $(Na^+)$ and potassium $(K^+)$ ions,and divalent magnesium $(Mg^{2+})$ and calcium $(Ca^{2+})$ ions are found in large proportions in biological fluids. These ions perform important biological functions such as the maintenance of ion balance and nerve impulse conduction.