The half-life of polonium is 140 days. In what time will 15 g of polonium be disintegrated out of its initial mass of 16 g?


Correct option is

560 days

Suppose the initial mass of a radioactive element is N0. The mass of the element left after n half-lives is given by 



The initial mass of polonium is . The mass of the disintegrated element is 15 g. So, the mass of the element left is . Thus   




The half-life of polonium is 140 days. Hence, the time taken in the disintegration of 15 g polonium is  

                                                        = 560 days.



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