<prompt> Which of the following is a naturally occuring radioactive substance in the body in small quantities?Radium 226Bismuth 60Iodine 131Potassium 40  <response>: Sources of radiation exposure are: Natural sources and Manmade sources. The natural sources include cosmic rays, environmental terrestrial and atmospheric radiation, internal radiation Potassium - 40 Carbon -14 Man-made Radiation: Medical and dental: X rays, radioisotopes Occupational exposure Nuclear Misc: TV, Radio-active dial watches, Luminous markers Parks Textbook of Preventive and Social Medicine, 25th Edition, Pg 803 