In coordination chemistry, ligands are categorized by their charge as neutral or charged. Neutral ligands possess no net charge, whereas charged ligands exhibit a positive or negative charge.
Step 1: Evaluate each option.
- \( \text{H}_2\text{O} \) (Water): Water is classified as a neutral ligand, lacking any overall charge.
- \( \text{NH}_3 \) (Ammonia): Ammonia is another example of a neutral ligand, with no net charge.
- \( \text{CO} \) (Carbon monoxide): Carbon monoxide is also a neutral ligand, frequently employed in transition metal complexes and without charge.
- \( \text{ONO} \) (Nitrito group): The nitrito group, \( \text{ONO}^- \), carries a negative charge and is therefore an anionic (charged) ligand, not neutral.
Step 2: Isolate the non-neutral ligand.
The ligand \( \text{ONO}^- \) is charged (specifically, negatively charged) and is consequently not neutral. This identifies it as the correct answer for a ligand that is not neutral.
Conclusion:
As the ligand \( \text{ONO}^- \) is not neutral, the correct designation is \( \mathbf{(C)} \).