1. On what type of bonds does CO insertion usually occur?

Metal−alkyl (M−R) bonds.

2. On what type of bonds does isonitrile insertion usually occur?

Metal−alkyl (M−R) and the metal−hydride (M−H) bonds.

3. On what type of bonds does C₂H₄ insertion usually occur?

Metal−hydride (M−H) bonds.

4. State an important requirement for the occurrence of an elimination reaction.

The presence of an adjacent vacant site.