In which of the following complexes oxidation state of metal is zero

• A

  $\left[\mathrm{Pt}{\left({\mathrm{NH}}_3\right)}_2{\mathrm{Cl}}_2\right]$

• B

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

• C

  $\left[\mathrm{Cr}{\left({\mathrm{NH}}_3\right)}_3{\mathrm{Cl}}_3\right]$

• D

  $\left[\mathrm{Cr}{\left(\mathrm{en}\right)}_2{\mathrm{Cl}}_2\right]$