NEET Physics Nuclei Questions Solved

A radioactive isotope X with a half-life of 1.37×109 years decays to Y which is stable. A sample of rock from the moon was found to contain both the elements X and Y which were in the ratio of 1 : 7. The age of the rock is
(a) 1.96×108 years         (b) 3.85×109 years
(c) 4.11×109years          (d) 9.59×109 years

(c) If in the rock there is no Y element, then the time taken by element X to reduce to 18th the initial value will be equal to 18=12nor n =3
Therefore, from the beginning three half life time is spent. Hence the age of the rock is

=3×1.37×109=4.11×109 years

Difficulty Level:

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