What indicates that sand is acceptable after washing with distilled water?

The indication that sand is acceptable after washing with distilled water is when the upper layer is clear and free of floating material. Washing with distilled water is meant to remove impurities and contaminants from the sand. When the water runs clear and there are no floating materials present, it shows that the washing process has effectively removed unwanted particles and organic matter. This clarity confirms the cleanliness of the sand, making it suitable for use in applications where purity is essential, such as in construction or as a filtration medium.

The other options suggest conditions that do not meet the cleanliness criteria required for acceptable sand. Discoloration or floating materials indicate that impurities remain, while a grainy appearance can also be misleading as graininess alone does not confirm cleanliness. A darker lower layer suggests sedimentation or the presence of impurities settled, which would not indicate acceptable sand quality.