Which among the following cations will form lowest stability complex if the ligand remains the same?

Which among following statements is true about $$\mathrm{Na}_4\left[\mathrm{Fe}(\mathrm{CN})_6\right]$$ ?

What is IUPAC name of $$[\mathrm{Co}(\mathrm{H}_2 \mathrm{O})(\mathrm{NH}_3)_5] \mathrm{I}_3$$ ?

What is effective atomic number of $$\mathrm{Pt}$$ in $$\left[\mathrm{Pt}\left(\mathrm{NH}_3\right)_4\right]^{2+}$$ ? (Given atomic number of $$\mathrm{Pt}=78$$)