The source of endogenous radiation is -: (A) Radon, (B) Potassium, (C) Thorium, (D) Uranium
Answer is B. Park's textbook of preventive and social medicine 23rd edition. * Man is also subjected to internal radiation,i.e, from radioactive matter stored in the body tissues, it includes minute quantities of uranium , thorium, isotopes of potassium,strontium and carbon.