ANS:D - 20

The dilution factor represents how much the original solution is diluted. A dilution factor less than 100 means that the solution is being diluted, but not to the extent where it's significantly weakened. If the dilution factor is less than 100, it means the concentration of the original solution is not being reduced by a large margin. So, among the options provided, the most accurate statement would be: "A nuisance is experienced in diluting water if dilution factor is less than 100." This implies that a dilution factor of 20, 40, 60, or 10 would all be considered a nuisance in diluting water, as they are all less than 100.