A very large quantity of mixture contains tiny particles of three different substances X, Y, and Z. They are of the same size, cubical in shape and yellow in colour. X particles are very heavy, insoluble, non-magnetic and contribute to 50% of the mixture. Y particles are very light, insoluble, non-magnetic and contribute to 40% of the mixture. And Z particles are actually iron pieces. Which of the following methods can separate X, Y more efficiently?