Which one is the highest melting halide?

Highest covalent character is found in

In the compounds $LiCl$,$RbCl$,$BeCl_2$,and $MgCl_2$,which of the following are the most and least ionic in nature,respectively?

The order of solubility of lithium halides in non-polar solvents follows the order:

The melting points of $(i)$ $BeCl_2$, $(ii)$ $CaCl_2$, and $(iii)$ $HgCl_2$ follow the order:

The charge/size ratio of a cation determines its polarizing power. Which one of the following sequences represents the increasing order of the polarizing power of the cationic species,$K^{+}, Ca^{2+}, Mg^{2+}, Be^{2+}$?