Answer: screen
A mixture of sand, salt and iron can be separated using magnet, filter paper and water. Iron being a magnetic material, can be separated using magnet. The rest of the mixture, salt and sand can be mixed in water. The salt would dissolve in water but sand would not because sand is insoluble in water. This mixture can be filtered using a filter paper. The filter has very minute openings through which sand would not pass through and get separated. Then, salty water can be heated. The water would evaporate leaving behind salt.
In this whole process, screen would not be useful because it would depend on the size of the sand particles and available screen.
