Correct answer is (a) 50-99%
For explanation I would say: Cyclone separators are generally able to remove somewhere in the range of 50-99% of all particulate matter. How well the cyclone separators are actually able to remove this matter depends largely on particle size. If there is large amount of lighter particulate matter, less of these particles are able to be separated out. Because of this, cyclone separators work best on flue gases that contain large amounts of big particulate matter.