To determine the number of incorrect statements from the given options, we will analyze each statement one by one.
### Step 1: Analyze Statement A
**Statement A:** The `pi` bond between metal and carbonyl carbon reduces the bond order of C-O in carbon monoxide.
- Carbon monoxide (CO) has a triple bond between carbon and oxygen, which means it has a bond order of 3.
- When CO acts as a ligand and forms a bond with a metal, it can donate electron density back to the metal through π-backbonding.
- This π-backbonding involves the metal donating electrons into the anti-bonding π* orbital of CO, which increases the number of electrons in the anti-bonding orbital.
- As a result, the bond order of C-O in CO decreases due to this interaction.
**Conclusion:** Statement A is **correct**.
### Step 2: Analyze Statement B
**Statement B:** `dz^(2)` orbital of central metal atom/ion is used in `dsp^(2)` hybridization.
- In `dsp²` hybridization, the orbitals involved are one d orbital, one s orbital, and two p orbitals.
- The `d` orbitals used in `dsp²` hybridization are typically the `dxy`, `dxz`, and `dyz` orbitals, which are in the same plane as the ligands.
- The `dz²` orbital is not involved in `dsp²` hybridization because it is oriented differently and does not participate in the bonding in this geometry.
**Conclusion:** Statement B is **incorrect**.
### Step 3: Analyze Statement C
**Statement C:** `CN^(-)` is a `pi_(-)` acid ligand.
- The cyanide ion (CN^(-)) is known to be a strong field ligand and acts as a π-acceptor ligand.
- It can accept electron density from the metal into its π* orbitals, making it a π-acidic ligand.
- Therefore, it is accurate to classify CN^(-) as a π-acid ligand.
**Conclusion:** Statement C is **correct**.
### Step 4: Analyze Statement D
**Statement D:** All negative ligands are stronger than neutral ligands.
- The strength of a ligand is not solely determined by its charge. It depends on various factors, including the ligand's ability to donate electron density and the overall electron availability.
- For example, while some negative ligands may be strong, others (like chloride, Cl^-) may not be as strong as certain neutral ligands (like CO).
- Therefore, it is incorrect to generalize that all negative ligands are stronger than neutral ligands.
**Conclusion:** Statement D is **incorrect**.
### Final Conclusion
- The incorrect statements are B and D.
- Therefore, the number of incorrect statements is **2**.
### Summary of Incorrect Statements:
- Statement B: Incorrect
- Statement D: Incorrect
### Final Answer:
The number of incorrect statements is **2** (B and D).
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