In complexes off wea field ligands, `Delta_(o) lt P` (pairing energy), the energy difference between `t_(2g) and e_(g)` sets is relatively less. Under the unfluence of strong field ligands, `Delta_(O) gt p` (Pairing energy), the energy difference between `t_(2g) and e_(g)` sets is relatively high.
Q. Select the correct statement regarding `[Cr(en)_(2)Cl_(2)]^(+) and [Co(C_(2)O_(4))_(2)(NH_(3))_(2)]^(-)` complex ions:

Options

A. Both are equally stable complexes
B. Both have equal number of stereoisomers
C. Both are diamagnetic complexes
D. a and c both

Answer

To solve the question regarding the complex ions \([Cr(en)_2Cl_2]^+\) and \([Co(C_2O_4)_2(NH_3)_2]^-\), we need to analyze the oxidation states, electronic configurations, and the nature of the ligands involved.

### Step-by-Step Solution:

1. **Determine the Oxidation State of Chromium in \([Cr(en)_2Cl_2]^+\)**:
- Ethylene diamine (en) is a neutral ligand, contributing 0 to the charge.
- Each chloride ion (Cl) has a charge of -1. Since there are 2 Cl ligands, they contribute -2 to the charge.
- Let the oxidation state of chromium be \(x\). The overall charge of the complex is +1.
- Therefore, the equation is:
\[ x + 0 + (-2) = +1 \implies x - 2 = 1 \implies x = +3 \]
- Thus, the oxidation state of chromium is +3.

2. **Determine the Electronic Configuration of Chromium**:
- The atomic number of chromium (Cr) is 24. The ground state electronic configuration is \([Ar] 3d^5 4s^1\).
- For \(Cr^{3+}\), we remove 3 electrons (2 from 4s and 1 from 3d):
\[ 3d^3 \]

3. **Determine the Oxidation State of Cobalt in \([Co(C_2O_4)_2(NH_3)_2]^-\)**:
- Oxalate ion \((C_2O_4)^{2-}\) is a bidentate ligand with a charge of -2. Since there are 2 oxalate ligands, they contribute -4 to the charge.
- Ammonia (NH3) is a neutral ligand, contributing 0 to the charge.
- Let the oxidation state of cobalt be \(y\). The overall charge of the complex is -1.
- Therefore, the equation is:
\[ y + (-4) + 0 = -1 \implies y - 4 = -1 \implies y = +3 \]
- Thus, the oxidation state of cobalt is +3.

4. **Determine the Electronic Configuration of Cobalt**:
- The atomic number of cobalt (Co) is 27. The ground state electronic configuration is \([Ar] 3d^7 4s^2\).
- For \(Co^{3+}\), we remove 3 electrons (2 from 4s and 1 from 3d):
\[ 3d^6 \]

5. **Analyze the Ligands**:
- Ethylene diamine (en) is a strong field ligand, which causes a large splitting of the d-orbitals.
- Oxalate ion (C2O4) is also a strong field ligand, but ammonia (NH3) is a moderate field ligand.
- Therefore, in \([Cr(en)_2Cl_2]^+\), the strong field ligand (en) will lead to a higher splitting energy (\(\Delta_o\)), while in \([Co(C_2O_4)_2(NH_3)_2]^-\), the combination of oxalate and ammonia will also lead to significant splitting.

6. **Determine Magnetic Properties**:
- \(Cr^{3+}\) with \(3d^3\) has unpaired electrons, making it paramagnetic.
- \(Co^{3+}\) with \(3d^6\) can be diamagnetic if all electrons are paired, which is likely in the presence of strong field ligands.

7. **Conclusion**:
- The correct statement regarding these complex ions is that they have different magnetic properties due to the different numbers of unpaired electrons.