Which one of the following has the highest molar conductivity?

The complex which produce more number of ions will have more molar conductivity. Here Potassium hexacyanoferrate (II) which is written as ${\mathrm{K}}_4\mathrm{Fe}{\left(\mathrm{CN}\right)}_6$ produces 4K+ and$[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6{]}_4$, it means it produces total 5 ions which is maximum among the given complexes. And hence option C is correct.