Among the following complexes (K to P),
$\begin{array}{l}{\mathrm{K}}_3\left[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6\right]\left(\mathrm{K}\right),\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_6\right]{\mathrm{Cl}}_3\left(\mathrm{L}\right),\\ {\mathrm{Na}}_3\left[\mathrm{Co}{\left(\text{oxalate}\right)}_3\right]\left(\mathrm{M}\right),\left[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]{\mathrm{Cl}}_2\left(\mathrm{N}\right),\\ {\mathrm{K}}_2\left[\mathrm{Pt}{\left(\mathrm{CN}\right)}_4\right]\left(\mathrm{O}\right),\text{ and }\left[\mathrm{Zn}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{P}\right)\end{array}$
The diamagnetic complexes are:

[K] : ${\mathrm{K}}_3\left[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6\right]:{\mathrm{Fe}}^{3+}$ has $3{\mathrm{d}}^5$ configuration; ${\mathrm{CN}}^{-}$ is strong field ligand and thus four electrons are paired leaving one unpaired electron with $d^{2}s{p}^3$ hybridization and thus paramagnetic.

[L]: $\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_6\right]{\mathrm{Cl}}_3:{\mathrm{Co}}^{3+}$ has configuration; ${\mathrm{NH}}_3$ is strong field ligand thus all six electrons are paired with ${\mathrm{d}}^2{\mathrm{sp}}^3$ hybridization and therefore diamagnetic.

[M]: $N{\mathrm{a}}_3\left[\mathrm{Co}{\left(\mathrm{ox}\right)}_3\right]:{\mathrm{Co}}^{3+}$ has $3{\mathrm{d}}^6$ configuration: ${\mathrm{C}}_2{\mathrm{O}}_4^{2-}$ is strong field ligand and thus all the six electrons are paired with ${\mathrm{d}}^2{\mathrm{sp}}^3$ hybridisation and therefore diamagnetic.
[N]: $\left[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]{\mathrm{Cl}}_2:{\mathrm{Ni}}^{2+}$ has $3{\mathrm{d}}^8$ configuration with two unpaired electrons. ${\mathrm{H}}_2\mathrm{O}$ is weak field ligand and thus ${\mathrm{sp}}^3{\mathrm{d}}^2$ hybridisation and paramagnetic.

[O]: ${\mathrm{K}}_2\left[\mathrm{Pt}{\left(\mathrm{CN}\right)}_4\right]:{\mathrm{Pt}}^{2+}$ has $3{\mathrm{d}}^8$ configuration; ${\mathrm{CN}}^{-}$ is strong field ligand and thus all the eight electrons are paired with ${\mathrm{dsp}}^2$ hybridisation and therefore diamagnetic. 
[P]: $\left[\mathrm{Zn}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]{\left({\mathrm{NO}}_3\right)}_2:{\mathrm{Zn}}^{2+}$ has $3{\mathrm{d}}^{10}$ configuration and thus all paired showing ${\mathrm{sp}}^3{\mathrm{d}}^2$ hybridization and so diamagnetic.