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

The first three options represent diagonal relationships in the periodic table: Li-Mg (Group 1, Period 2 with Group 2, Period 3), Be-Al (Group 2, Period 2 with Group 13, Period 3), and B-Si (Group 13, Period 2 with Group 14, Period 3). Diagonal relationships arise because moving diagonally across the periodic table results in similar charge-to-size ratios, leading to similar chemical properties.

However, Li-Na are both elements in Group 1 (alkali metals). This is not a diagonal relationship but rather a relationship within the same group. While elements in the same group share some properties, this is a fundamentally different type of relationship compared to the diagonal pairs listed in the other options.

Therefore, Li-Na differs in its mutual relationship from the other sets, which are all diagonal pairs.