Explain why both a power source (like a battery) and a complete circuit are necessary for an electromagnet to function. 

So that the electromagnet can work.

Explanation:

Electromagnets use electricity to function.

2h2o2--> 2h2o + o2

this reaction is of the spontaneous decomposition of hydrogen peroxide down into water and oxygen.

add 2 molecules of hydrogen peroxide and 2 molecules of water. since oxygen is naturally diatomic, the total number of atoms of each element is now the same on both sides of the equation so it is balanced.

this may not be entirely correct but let me know.