A few drops of iodine solution were added to rice water. The solution turned blue-black in colour. This indicates that the rice water contains:

Solution of Iodine is often used for testing the presence of starch in the food particles, as we know that. But, when iodine is added to starch, it turns blue-black. rice water it turns blue-black because it contains starch, hence when iodine solution is added to rice water it turns blue-black. You must have also done such a science experiment.