1. Goal: Find the complex with the highest paramagnetic behaviour, i.e. the one with the maximum number of unpaired electrons.

2. Check each complex one by one.

Option A: $[Fe(en)(bpy)(NH_3)_2]^{2+}$

• Oxidation state of Fe:

  • $en$, $bpy$, $NH_3$ are all neutral ligands.
  • Therefore, Fe is in $+2$ oxidation state.

• Electronic configuration: $Fe^{2+} : 3d^6$

• Nature of ligands:

  • $en$ and $bpy$ are strong field ligands.
  • $NH_3$ is also reasonably strong compared to weak ligands.

So this is expected to be a low-spin octahedral complex: $t_{2g}^6 e_g^0$

• Number of unpaired electrons $=0$.

So, A is diamagnetic.

Option B: $[Pd(gly)_2]$

• Glycinato $(gly^-)$ is a mononegative bidentate ligand.

• Two $gly^-$ ligands contribute $-2$, and the complex is neutral.

• Hence oxidation state of Pd is: $x-2=0 \Rightarrow x=+2$

• Electronic configuration: $Pd^{2+} : 4d^8$

• For $4d$ metals, pairing is generally strong; $Pd(II)$ commonly forms square planar complexes.

• Square planar $d^8$ complexes are typically diamagnetic.

• Number of unpaired electrons $=0$.

So, B is diamagnetic.

Option C: $[Co(OX)_2(OH)_2]^-$ with $(\Delta_o > P)$

• Let oxidation state of Co be $x$.
• Oxalate $(OX^{2-})$: two ligands give $-4$.
• Two $OH^-$ give $-2$.
• Overall charge is $-1$.

Thus, $x-4-2=-1$ $x=+5$

So cobalt is $Co^{5+}$.

• Electronic configuration:
  • Co: $[Ar]3d^7 4s^2$
  • $Co^{5+} : 3d^4$

Given $\Delta_o > P$, it is a low-spin octahedral complex.

For low-spin $d^4$ octahedral: $t_{2g}^4 e_g^0$

This gives 2 unpaired electrons.

So, C is paramagnetic with 2 unpaired electrons.

Option D: $[Ti(NH_3)_6]^{3+}$

• $NH_3$ is neutral, so Ti is in $+3$ oxidation state.

• Electronic configuration: $Ti^{3+} : 3d^1$

In octahedral field: $t_{2g}^1 e_g^0$

• Number of unpaired electrons $=1$.

So, D is paramagnetic with 1 unpaired electron.

3. Compare number of unpaired electrons:

• A: $0$
• B: $0$
• C: $2$
• D: $1$

Hence, the complex showing the highest paramagnetic behaviour is: $\boxed{[Co(OX)_2(OH)_2]^-}$

So, Option C is correct.

4. Comparison with stored answer:

• Stored correct answer: C
• Derived answer: C

They agree.