ANSWER:
Container A (10 L)
Explanation:
The heat energy depends on several things, among the most important we have the temperature, mass and phase of the substance.
Since both containers contain liquid water at the same temperature, we rule out and only the mass is relevant, therefore a greater mass would have greater heat energy.
Now, we can say that they have the same density, therefore, the greater the volume, the greater the mass. Which means, a container with 10 L of water would have higher heat energy than one with 2L.