The sire of Respirable dust is -

Ans. is 'a' i.e., 1-5 microns Pneumoconiosis Pneumoconiosis is an occupational lung disease caused by the inhalation of dust. o The development of pneumoconiosis depends on - i) The amount of dust retained in the lungs and airways. ii) The size, shape of the paicles --> The most dangerous paicle ranges from 1 to 5 in in diameter because they may reach the terminal small airway and air sacs and settle in their linings. iii) Paicle solubility and physiochemical reactivity. iv) Additional effects of other irritants (e.g. concomitant smoking).