Which statement about free surface is considered true?

The statement regarding pocketing occurring at small angles of inclination when a tank is 98% full is accurate because it reflects the influence of free surface effects on vessel stability. When a tank is nearly full, the liquid inside can create a condition where the movement of the fluid can cause shifts in the center of gravity and the center of buoyancy of the vessel. At small angles of inclination, even a slight movement of the fluid can lead to a change in the righting moments and contribute to a reduction in stability. This phenomenon, known as pocketing, describes how the dynamics of nearly full tanks can impact the overall stability of the vessel.

Other options present misconceptions about free surface effects. The presence of free surface actually reduces stability as it creates a shifting weight, which can negatively affect the vessel's ability to return to an upright position after being tilted. Free surface does have a significant effect on a tank's stability; thus, claiming it has no effect is not correct. Furthermore, free surface corrections are not constant because they vary with the amount of liquid in the tank and the tank's configuration, contradicting the claim that they are constant regardless of tank content.