Which of the following statements is correct about sedimentation of a given soil?

When a soil sample is mixed with water, shaken vigorously, and allowed to stand, the particles separate into distinct layers based on their size and density. This process is called sedimentation.

During sedimentation, the heaviest and largest particles (gravel and coarse sand) settle first and form the bottom layer. Medium-sized particles (fine sand and silt) settle above them, and the finest particles (clay) settle on top of the mineral layers because they are the lightest solid particles. Decaying organic matter (humus) has a lower density than the mineral particles and water, so it floats on the surface of the water rather than sinking.

The correct statement is that decaying organic matter remains afloat. This is because humus particles are light and often contain trapped air, giving them a density lower than that of water.

The statement that the largest and medium-sized particles settle at the bottom is partially true (the largest do settle at the bottom), but it is imprecise because it groups two different size classes without noting that they form separate layers. The claim that decaying organic matter settles at the bottom contradicts what actually happens - humus floats. The claim that the largest soil particles remain suspended in water is incorrect because large particles are the first to settle due to their greater weight.