Question 20: Vinh conducts an experiment as follows: You use a distillation device to bring 100 ml of water to a boil, then lead the steam through the cooling system so that it condenses to form distilled water. You put distilled water into four cups, 20ml each. Next, you put in cups 1, 2, 3, 4 respectively 2, 4, 6, 8 g of salt and stir well. You noticed: How to identify a pure substance?
To identify a substance as pure, we can simply check based on the physical properties of the substance.
The answer to choose is: EASY