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Half lives of two isotopes X and Y of a material are known to be `2 xx 10^(9)` years and `4 xx 10^(9)` years respectively. If a planet was formed with equal number of these isotopes, then the current age of planet, given that currently the material has 20 % of X and 80 % of Y by number, will beA. `2 xx 10^(9)` yearsB. `4 xx 10^(9)` yearsC. `6 xx 10^(9)` yearsD. `8 xx 10^(9)` years |
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Answer» Correct Answer - D `N=(N_(0))/(2).e^(-lamda_(1)t)=0.2 N_(0)` `N_(y) =(N_(0))/(2) e^(-lamda_(2) t) = 0.8 N_(0)` `e^((lamda_(1)-lamda_(2)))=4 rArr t=8xx10^(9)` years |
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