a) When raisins are placed in water at room temperature, the raisins will swell up as the water enters the cells of the raisins. This happens due to osmosis. The concentration of water is higher on the outside than on the inside of the raisins.
b) When raisins are places in water at 4°C, they will swell up as the water enters the cells due to osmosis. But, due to the low temperature, the rate at which water enters the raisins is slower than that at room temperature.
c) When raisins are placed in a concentrated sugar solution, the raisins will wilt and shrink. This is due to osmosis or exosmosis, wherein the water moves from the inside of the cell (less concentrated) to the outside which is more concentrated with sugar.