A. According to the floating and sinking conditions of objects, as shown in Figure 2, when an egg floats in salt water, the buoyancy force is equal to gravity. Therefore A is wrong;

B. Figure 2, as the solvent in the brine slowly evaporates, the concentration of the brine increases and the density increases, but the egg is still floating and the buoyancy force it experiences remains unchanged. According to F float = ρ liquid gV discharge, it can be seen that the volume of the salt water displaced by the egg becomes smaller, so the volume of the immersed part will become smaller and smaller. Therefore, B is wrong;

C. According to the floating and sinking conditions of the object, when the object continues to float in salt water in Figure 3, the buoyancy force is equal to gravity. Therefore, C is wrong;

D. Both the egg in Figure 2 and the egg in Figure 3 are in a floating state, and the buoyancy force is equal to its gravity. The gravity of the egg remains unchanged, and the buoyancy force it experiences remains unchanged. Therefore, the buoyancy force experienced by the egg in Figure 2 is the same as that of the egg in Figure 2. Figure 3: The buoyancy force on the eggs is the same. Therefore D is correct.

Therefore choose D.