Which of the following species is not expected to be a ligand?

Options

A. `NO`
B. `NH_(4)^(+)`
C. `NH_(2)CH_(2)CH_(2)NH_(2)`
D. `CO`

Answer

To determine which of the given species is not expected to be a ligand, we need to analyze each option based on their ability to donate a lone pair of electrons to a central metal atom. Ligands are typically electron pair donors that can form coordinate bonds with metal ions.

### Step-by-Step Solution:

1. **Identify the Options**: The species provided are:
- N-O
- NH4+
- NH2
- CO

2. **Understand Ligand Properties**: A ligand must have at least one lone pair of electrons that it can donate to a metal ion.

3. **Analyze Each Option**:
- **N-O**: This species has nitrogen and oxygen, both of which typically have lone pairs of electrons. Therefore, it can act as a ligand.
- **NH4+**: This species is the ammonium ion. It has a positive charge and all four valencies of nitrogen are satisfied by hydrogen atoms. There are no lone pairs available for donation, so it cannot act as a ligand.
- **NH2**: The amine group (NH2) has a lone pair of electrons on the nitrogen atom, which can be donated to a metal ion, making it a potential ligand.
- **CO**: Carbon monoxide has a lone pair of electrons on the carbon atom that can be donated to a metal ion, thus it can also act as a ligand.

4. **Conclusion**: Among the options, NH4+ is the only species that does not have a lone pair of electrons to donate. Therefore, it is not expected to be a ligand.

### Final Answer:
**NH4+ is not expected to be a ligand.**