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Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
Rahul kumar
Answer: 2 half lifes Half life for any radio nuclei is the time after which half of the parent radioactive isotopes decay to produce daughter nuclei. After one half life; Ratio of parent to stable daughter = 1:1 After 2 half lifes, Ratio of parents to stable daughter = 0.5 / (1 + 0.5) = 0.5 / 1.5 = 1/3 (same as in question) So, the answer should be 2 half lifes.