(a) Both Li and Mg are harder and lighter than the other metals in their respective groups. (b) Li like Mg decomposes water slowly to liberate hydrogen. 2Li + $2H_2O$ → 2LiOH + $H_2$ ↑ Mg + $2H_2O$ → $Mg(OH)_2 + H_2$ ↑ The hydroxides so formed are weak bases and decompose on heating. 2LiOH → $Li_2O + H_2O$ ; $Mg(OH)_2$ → MgO + $H_2O$ (c) Both form nitrides upon direct combination with nitrogen gas. 6Li + $N_2$ → $2Li_3N$ ; 3Mg + $N_2$ → $Mg_3N_2$ (d) Both form monoxides when heated in oxygen. 4Li + $O_2$ → $2Li_2O$ ; 2Mg + $O_2$ → 2MgO The oxides do not combine with excess oxygen to give superoxides. (e) Carbonates of Li and Mg decompose on heating. $Li_2CO_3$ → $Li_2O + CO_2$ ; $MgCO_3$ → MgO + $CO_2$ (f) Both LiCl and $MgCl_2$ are soluble in ethanol, they are deliquescent and crystallise from aqueous solution as hydrates, $LiCl . 2H_2O$ and $MgCl2_ . 6H_2O$.