As coal is heated, some of the molecules move so fast that they are destroyed. Some of the energy in coal is destroyed by the intense heat required to release its potential energy. Some of the potential energy in coal is converted into forms of energy other than electricity. The amount of potential energy in fuels is overestimated.
I gave my students this multiple choice question: When coal is burned to produce electricity, the electrical energy produced is less than the potential energy in the coal. Which best explains this observation?

Only one answer is correct among these 4 choices:
- As coal is heated, some of the molecules move so fast that they are destroyed.
- Some of the energy in coal is destroyed by the intense heat required to release its potential energy.
- Some of the potential energy in coal is converted into forms of energy other than electricity.
- The amount of potential energy in fuels is overestimated.

Could you tell me which one is correct?

Some of the potential energy in coal is converted into forms of energy other than electricity.