Final answer:
To reduce the force necessary to open the hatch at depth, option B) Decrease the pressure inside the bell is correct, as it will reduce the pressure differential across the hatch, making it easier to open.
Step-by-step explanation:
To reduce the force necessary to open the hatch of a submarine or a diving bell at depth, you would need to consider the difference in pressure on each side of the hatch. The pressure outside the hatch increases with depth due to the weight of the water above it, following the relation p = hρg, where p is the pressure, h is the depth, ρ is the density of the fluid, and g is the acceleration due to gravity. In this case, the correct answer to the question is B) Decrease the pressure inside the bell. This would reduce the pressure differential across the hatch, making it easier to open. The other options, such as increasing the surface area of the hatch or adding weights, do not influence the pressure differential and, thus, would not be effective. Increasing the volume of the bell's interior would not change the pressure differential either unless it somehow leads to a change in internal pressure.