Correct!

Please review the explanation below:

Answer: 3

To be buoyant, an object must displace an amount of liquid at least equal to its weight. Any action that makes the tank heavier than the weight of the liquid it displaces will prevent the tank from floating. All the alternatives except (3) will make the tank heavier than the weight of the liquid displaced. Therefore, only (3) will allow the tank to float off the bottom of the pit.