$\left[\mathrm{Pt}{\left({\mathrm{NH}}_3\right)}_2\mathrm{Cl}\left({\mathrm{NO}}_2\right)\right]$ :-

Let the oxidation number of platinum = $\mathrm{x}$

Ammonia is a neutral ligand and chloride is having the $-1$ oxidation number and nitrate has the $-1$oxidation number.

$$\begin{gathered} \mathrm{x}+2\times \left(0\right)+\left(-1\right)+\left(-1\right)=0 \\ \mathrm{x}-2=0 \\ \mathrm{x}=+2 \end{gathered}$$

Hence, the oxidation state of platinum is $+2$.

${\left[{\mathrm{CoCl}}_2(\mathrm{en}{)}_2\right]}^{\oplus }:-$

Let the oxidation number of cobalt = $\mathrm{y}$

Ethylenediamine is a neutral ligand and chloride has the $-1$ charge.

So,

$$\begin{gathered} \mathrm{x}+2\left(-1\right)=+1 \\ \mathrm{x}=+3 \end{gathered}$$

Hence, the oxidation number of central metal in $\left[\mathrm{Pt}{\left({\mathrm{NH}}_3\right)}_2\mathrm{Cl}\left({\mathrm{NO}}_2\right)\right]$ and ${\left[{\mathrm{CoCl}}_2(\mathrm{en}{)}_2\right]}^{\oplus },$ respectively, are $+2;+3$.