Give the number of ligand(s) which is//are non-classical ligand
`CO, NO, C_(2)H-(4),C_(3)H_(5) Θ , H^(Θ)` .

Explanation

To determine the number of non-classical ligands from the given options (CO, NO, C2H4, C3H5, and H), we will analyze each ligand based on the definition of non-classical ligands.

### Step-by-Step Solution:

1. **Understanding Non-Classical Ligands**:
- Non-classical ligands, also known as π-acidic ligands, can donate sigma (σ) electrons and accept pi (π) electrons. They have empty orbitals of suitable symmetry and energy that can interact with the d-orbitals of the central metal atom.

2. **Analyzing Each Ligand**:
- **CO (Carbon monoxide)**:
- CO is a well-known non-classical ligand. It donates a pair of electrons (σ donation) from the carbon atom and can accept π electrons due to its empty π* orbitals.
- **Conclusion**: CO is a non-classical ligand.

- **NO (Nitric oxide)**:
- NO can act as a non-classical ligand as it has a lone pair of electrons that can be donated (σ donation) and can also accept π electrons due to its empty π* orbitals.
- **Conclusion**: NO is a non-classical ligand.

- **C2H4 (Ethylene)**:
- C2H4 can act as a non-classical ligand because it has a π bond that can donate electrons and can also accept π electrons from the metal center.
- **Conclusion**: C2H4 is a non-classical ligand.

- **C3H5 (Propene)**:
- C3H5 can also act as a non-classical ligand. It has a π bond that can participate in π-backbonding with the metal, allowing it to accept π electrons while donating σ electrons.
- **Conclusion**: C3H5 is a non-classical ligand.

- **H (Hydrogen)**:
- Hydrogen does not have the ability to donate π electrons or accept them. It can only donate a single σ electron.
- **Conclusion**: H is not a non-classical ligand.

3. **Counting Non-Classical Ligands**:
- From the analysis, we have identified CO, NO, C2H4, and C3H5 as non-classical ligands. H is not included.
- Therefore, the total number of non-classical ligands is 4.

### Final Answer:
The number of non-classical ligands is **4**.

---