The stabilization of coordination compounds due to chelation is called the chelate effect. Which of the following is the most stable complex species?

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

1.  NO

2.  NH${}_4^{+}$

3.  NH${}_2$CH${}_2$CH${}_2$NH${}_2$

4.  CO

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

1. NO

2. NH${}_4^{+}$

3. ${\mathrm{NH}}_2{\mathrm{CH}}_2{\mathrm{CH}}_2{\mathrm{NH}}_2$

4. CO