Give the number of ligand(s) which is/are non-classical ligand an `pi` donor as well as pi acceptor ligand
`CO,PH_(3), PF_(3),C_(3)H_(5)^(Θ) ,C_(5)H_(5) Θ` .

Explanation

To solve the question, we need to identify the ligands from the given list that are non-classical ligands and can act as both π donors and π acceptors.

### Step-by-Step Solution:

1. **Understanding Non-Classical Ligands**:
- Non-classical ligands are those that can donate electron density through π bonds and can also accept electron density into their empty π* (pi star) orbitals.
- For a ligand to be classified as a non-classical ligand, it must have an empty π* orbital that can accept electrons.

2. **Analyzing Each Ligand**:
- **CO (Carbon Monoxide)**:
- CO has a lone pair on carbon which allows it to act as a π donor.
- It also has a π* orbital that can accept electrons, making it a non-classical ligand.
- **PH₃ (Phosphine)**:
- PH₃ does not have a π* orbital; it primarily acts as a σ donor.
- Therefore, it cannot be classified as a non-classical ligand.
- **PF₃ (Phosphorus Trifluoride)**:
- PF₃ has a lone pair on phosphorus which allows it to act as a π donor.
- It also has empty π* orbitals that can accept electrons, qualifying it as a non-classical ligand.
- **C₃H₅⁻ (Propyl anion)**:
- C₃H₅⁻ does not have a π* orbital and primarily acts as a σ donor.
- Hence, it is not a non-classical ligand.
- **C₅H₅⁻ (Cyclopentadienyl anion)**:
- C₅H₅⁻ has delocalized π electrons but does not have empty π* orbitals available for accepting electrons.
- Thus, it cannot be classified as a non-classical ligand.

3. **Conclusion**:
- After analyzing all the ligands, we find that the ligands that are non-classical and can act as both π donors and π acceptors are:
- CO and PF₃.
- Therefore, the total number of ligands that meet the criteria is **2**.

### Final Answer:
The number of ligands which are non-classical ligands and π donors as well as π acceptors is **2** (CO and PF₃).

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