Statement I : Li and Mg both produce nitride with nitrogen on heating
Statement II : Li and Mg both have outer most electron in s - subshell

→ Due to the same polarising power of Li⁺ & Mg⁺² they show diagonal relationship
Due to the diagonal relationship they shows certain similarites
Eg: Both Li & Mg reacts with atmospheric nitrogen and produces respective nitrides

$$\begin{gathered} 6\mathrm{Li}+{\mathrm{N}}_2\to \underset{\mathrm{Lithium} \mathrm{nitride}}{2{\mathrm{Li}}_3\mathrm{N}} \\ 3\mathrm{Mg}+{\mathrm{N}}_2\to \underset{\mathrm{Magnesium} \mathrm{nitride}}{{\mathrm{Mg}}_3{\mathrm{N}}_2} \end{gathered}$$
→₃Li    1s² 2s¹
   ₁₂Mg  1s² 2s² 2p⁶ 3s²
Both Li & Mg have last electron in S-subshell
$\therefore$ Statement - I & Statement - II are correct