The set of elements that differ in mutual relationship from those of the other sets is :

$\mathrm{Li}-\mathrm{Mg}, \mathrm{B}-\mathrm{Si}, \mathrm{Be}-\mathrm{Al}$ show diagonal relationship but $\mathrm{Li}$ and $\mathrm{Na}$ do not show diagonal relationship as both belongs to same group and not placed diagonally.