1. Find oxidation state of Cr in $[Cr(H_2O)_6]Cl_3$

   • The complex is $[Cr(H_2O)_6]^{3+}$ with $3Cl^-$ outside.
   • $H_2O$ is a neutral ligand.

   Let oxidation state of Cr be $x$. $x+6(0)=+3$ $x=+3$

2. Find oxidation state of Cr in $[Cr(C_6H_6)_2]$

   • Benzene, $C_6H_6$, acts as a neutral ligand in arene complexes.

   Let oxidation state of Cr be $x$. $x+2(0)=0$ $x=0$

3. Find oxidation state of Cr in $K_2[Cr(CN)_2(O)_2(O_2)(NH_3)]$

   • Since there are $2K^+$ ions, the complex ion has charge $-2$.
   • Ligand charges:
     • $2CN^- \Rightarrow -2$
     • $2O^{2-} \Rightarrow -4$
     • $O_2^{2-}$ (peroxo ligand) $\Rightarrow -2$
     • $NH_3 \Rightarrow 0$

   Let oxidation state of Cr be $x$. $x+(-2)+(-4)+(-2)+0=-2$ $x-8=-2$ $x=+6$

4. Thus the oxidation states are $+3,\ 0,\ +6$

5. Check options

   • A: $+3, 0, +4$ ❌
   • B: $+3, +4, +6$ ❌
   • C: $+3, +2, +4$ ❌
   • D: $+3, 0, +6$ ✅

Therefore, the correct option is D.