Question

what is a characteristic of all fuel cells? energy from the sun is converted into electricity. electrical energy is produced from oxidation reactions. oxidation reactions are used to produce thermal energy. a constant source of energy is not required.

Explanation:

1. Analyze Option 1: Solar cells convert solar energy to electricity, not fuel cells. So this is incorrect.
2. Analyze Option 2: Fuel cells work by oxidation - reduction reactions (redox reactions), where oxidation reactions (along with reduction) produce electrical energy. This matches the function of fuel cells.
3. Analyze Option 3: Fuel cells are mainly for producing electrical energy, not thermal energy (though some heat is produced, it's not the main purpose of all fuel cells). So this is incorrect.
4. Analyze Option 4: Fuel cells require a constant source of fuel (like hydrogen, methanol etc.) and an oxidant (like oxygen) to keep the reaction going. So a constant source of energy - related substances is required. This is incorrect.

Answer:

B. Electrical energy is produced from oxidation reactions.