Here's a problem to solve: When a mixture of oxygen and hydrogen is ignited in a test tube, the reaction shown occurs. Hydrogen + Oxygen -> Water + Energy What happens to the total mass of the contents of the test tube?

Among the 4 following options, which is the correct answer?

- A: The total mass increases.
 
- B: The total mass decreases.
 
- C: The total mass remains the same.
 
- D: Part of the mass is changed to heat energy.
 