Dry raisins were soaked in water for 2 hours, to determine the percentage of water absorbed by raisins. Before final weighing of swollen raisins, the extra water left on the surface of soaked raisins was removed by :

To determine the percentage of water absorbed by raisins, we need to measure the mass of the swollen raisins accurately. Any extra water adhering to the surface of the soaked raisins will add to their final weight, leading to an incorrect, higher value. Therefore, the surface water must be removed. Using a filter paper (Option D) is the standard laboratory method because it gently blots and absorbs the surface moisture without squeezing the raisins or causing them to lose the water they have absorbed. Option A (gently rubbing with cotton cloth) or Option C (dry cotton wool) can leave fibers on the sticky surface of the raisins or apply uneven pressure. Option B (hot air blower) can cause evaporation of the water absorbed inside the raisins due to heat, altering the results.