Which of the following system has the maximum number of unpaired electrons?

Choose the complex, which is paramagnetic

(i) ${\left[\mathrm{Fe}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{2+}$

(ii) ${\mathrm{K}}_3\left[\mathrm{Cr}{\left(\mathrm{CN}\right)}_6\right]$

(iii) ${\mathrm{K}}_3\left[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6\right]$

(iv) ${\mathrm{K}}_2\left[\mathrm{Ni}{\left(\mathrm{CN}\right)}_4\right]$

For the complex ${\mathrm{ML}}_2,$ stepwise formation constants for $\mathrm{M}+\mathrm{L}\rightleftharpoons \mathrm{ML}$ and $\mathrm{ML}+\mathrm{L}\rightleftharpoons {\mathrm{ML}}_2$ are $4$ and $3$, respectively. Hence, the overall stability constant for $\mathrm{M}+2\mathrm{L}\rightleftharpoons {\mathrm{ML}}_2$ is