Which of the following compounds exhibits the highest covalent character?

The ascending order of polarizing power of the following ions is:
\(\mathrm{K}^{+}, \mathrm{Ca}^{2+}, \mathrm{Mg}^{2+}, \mathrm{Be}^{2+}\)

1. Mg²⁺ < Be²⁺ < K⁺ < Ca²⁺

2. Be²⁺ < K⁺ < Ca²⁺ < Mg²⁺

3. K⁺ < Ca²⁺ < Mg²⁺< Be²⁺

4. Ca²⁺ < Mg²⁺ < Be²⁺ < K⁺