To separate out a mixture containing ammonium chloride, sodium chloride and magnesium carbonate, we can use their properties, specifically water solubility and decomposition behavior. Magnesium carbonate is insoluble in water, sodium chloride is soluble in water and ammonium chloride decomposes at higher temperature.
Add water to the mixture and mix it. Magnesium carbonate will not mix and hence can be filtered out. Heat the remaining solution to about 350 degrees Celsius. At this temperature ammonium chloride appears to sublimate. It actually breaks down into ammonia and hydrochloric acid. We can collect the gases to recover it. Sodium chloride has a higher melting (801 degrees Celsius) than ammonium chloride (338 degrees Celsius) and hence can be recovered directly.
This way we can separate out the three compounds from the mixture.
Hope this helps.