If tanks containing liquid lie below the waterline, what should be the position of the cross-connection valve?

When tanks containing liquid lie below the waterline, the position of the cross-connection valve is indeed critical for stability and operational safety. The correct answer indicates that it makes no difference whether the valve is open or closed.

This is because having the tanks submerged means that water pressure acts on the liquid in the tanks, and the hydraulic equilibrium between the liquid in the tanks and the surrounding water helps maintain stability regardless of the valve position. If the valve is open, the liquid can freely move between the tanks, which can help ensure even distribution. Conversely, if the valve is closed, the liquid remains static within the tank, which also contributes to stability.

In either case, the fundamental principles of fluid dynamics apply, and the pressures will balance out. Since the question specifically focuses on tanks positioned below the waterline, the impact of the valve position on stability becomes secondary to the conditions caused by submersion.

While other choices suggest more restrictive operational practices, they overlook the fact that stability in this context relies more on the positioning of the tanks and the overall design of the vessel rather than merely the state of the cross-connection valve.