Which of the following contain one unpaired electron in the 4p orbitals?

Which of the following complexes are low spin and diamagnetic?

$\left(\mathrm{a}\right)$ ${\mathrm{K}}_4\left[\mathrm{Os}(\mathrm{CN}{)}_6\right]$

$\left(\mathrm{b}\right)$ $\left[\mathrm{Mo}{\left(\mathrm{CO}\right)}_6\right]$

$\left(\mathrm{c}\right)$ ${\left[\mathrm{Mn}(\mathrm{CN}{)}_6\right]}^{4-}$

Select the correct answer using the codes given below:

Arrange the following in order of decreasing number of unpaired electrons.

(I) ${\left[\mathrm{Fe}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{2+}$    (II) ${\left[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6\right]}^{3-}$    (III) ${\left[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6\right]}^{4-}$   (IV) ${\left[\mathrm{Fe}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{3+}$