A student set up an experiment to investigate diffusion. A block of agar, 1.0 cm × 1.0 cm × 1.0 cm, was stained uniformly with a water-soluble blue dye. The block of agar was put into a test-tube containing 10 cm³ of distilled water at 20 °C. The intensity of the blue colour of the water after five minutes was measured. Four other experiments, A, B, C and D, were then carried out using different numbers of agar blocks, different sizes of agar blocks and different temperatures. All other variables were standardised. Which experiment would give a lighter blue colour in the water after five minutes compared to the first experiment? [Table showing size of each agar block/cm, number of agar blocks, temperature of distilled water/°C]

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