Which of the following has the lowest melting point?

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

Which one is the highest melting halide?

Highest covalent character is found in

Which of the following halides has the highest melting point?

Which of the following orders is incorrect?