Which of the following orders is incorrect for the properties indicated against each ?

Options

A. `[Cr(NH_(3))_(6)]^(3+) gt [Mn(CN)_(6)]^(3-) gt [V(CO)_(6)]" "-` magnetic moment (spin only values in B.M.)
B. `[Co(CN)_(6)]^(3-) gt [Co(NH_(3))_(6)]^(3+) gt [Co(H_(2)O)_(6)]^(3+)" "-Delta_(0)` values
C. `[Ni(CO)_(4)] gt [Co(CO)_(4)]^(-) gt [Fe(CO)_(4)]^(2-)" "-` strength of `M-Cpi` bond.
D. `[Fe(CN)_(6)]^(3-) lt [Co(CN)_(6)]^(4-) lt [Ni(NH_(3))_(6)]^(2+)" "-` effective atomic number of metal ion.

Explanation

To solve the question regarding which order is incorrect for the properties indicated, we will analyze each property step by step.

### Step 1: Analyze Magnetic Moment
- **Magnetic Moment** is determined by the number of unpaired electrons in the d-orbitals of the metal ion.
- For the given metal ions:
- **Cr³⁺** (3d³): 3 unpaired electrons
- **Mn²⁺** (3d⁴): 4 unpaired electrons
- **V³⁺** (3d²): 2 unpaired electrons
- The order of magnetic moments based on the number of unpaired electrons is:
- Mn²⁺ > Cr³⁺ > V³⁺

**Conclusion**: This order is correct.

### Step 2: Analyze Delo Value
- **Delo Value** refers to the splitting of d-orbitals due to ligand field effects.
- The order of Delo values is influenced by the strength of the ligands according to the spectrochemical series.
- Strong field ligands cause greater splitting, leading to higher Delo values.
- If the order is given as incorrect, we need to check if it aligns with the ligand strength.

**Conclusion**: The order of Delo values is generally correct if based on the spectrochemical series.

### Step 3: Analyze Strength of M-Cl Bond
- The strength of the M-Cl bond depends on the ability of the metal to stabilize the bond through its electronic configuration and charge.
- The order of bond strength typically follows the trend of the metal's ability to stabilize the bond.
- If the order given is inconsistent with known trends in bond strength, it can be deemed incorrect.

**Conclusion**: This order may be incorrect if it does not follow the expected trends.

### Step 4: Analyze Effective Atomic Number (EAN)
- **Effective Atomic Number (EAN)** is calculated as the total number of protons in the metal ion plus the number of electrons donated by the ligands.
- For the complexes:
- For Fe²⁺ (26 protons) with 12 electrons from ligands: EAN = 26 + 12 = 38
- For Co²⁺ (27 protons) with 12 electrons from ligands: EAN = 27 + 12 = 39
- For Ni²⁺ (28 protons) with 12 electrons from ligands: EAN = 28 + 12 = 40
- The order of EAN should be: Ni > Co > Fe.

**Conclusion**: This order is correct.

### Final Conclusion
After analyzing all properties, the incorrect order is likely related to the strength of the M-Cl bond. Therefore, the answer to the question is that the incorrect order is found in the property of the strength of the M-Cl bond.

### Answer: Option 3 is the incorrect order.

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