You are presented with the question "What bonds cause H2O to expand when freezing?" and the following answer choices: 
- Covalent
 - Hydrogen
 - Metallic
 - an ion
 - Heat energy
 - Ionic
 - heat
 - an anion

Now knowing that hydrogen bonds cause water to expand when it freezes and water is made up of H2O molecules, choose the best answer.


 

  Hydrogen       