Coordination Compounds

Atomic number of \(\mathrm{Mn}, \mathrm{Fe}\) and \(\mathrm{Co}\) are 25, 26 and 27 respectively. Which of the following inner orbital octahedral complex ions are diamagnetic?

I. \(\left[\mathrm{CO}\left(\mathrm{NH}_3\right)_6\right]^{3+}\)

II. \(\left[\mathrm{Mn}(\mathrm{CN})_6\right]^{3-}\)

III. \(\left[\mathrm{Fe}(\mathrm{CN})_6\right]^{4-}\)

IV. \(\left[\mathrm{Fe}(\mathrm{CN})_6\right]^{3-}\)

Choose the correct option.