(N/A) The resemblance between $Li$ and $Mg$ is due to the diagonal relationship in the periodic table, which arises from their similar ionic radii and charge-to-size ratios (ionic potential).
$1$. Both $Li$ and $Mg$ react slowly with water. Their oxides and hydroxides are much less soluble in water compared to other alkali and alkaline earth metals, and their hydroxides decompose on heating.
$2$. Both elements form nitrides by direct combination with nitrogen, i.e., $Li_3N$ and $Mg_3N_2$.
Reason: This similarity is primarily due to their comparable ionic radii ($Li^+ = 76 \text{ pm}$ and $Mg^{2+} = 72 \text{ pm}$) and similar electronegativity values, which lead to similar polarizing power.