The half life of a radioactive isotope ‘X’ is 20 years. It decays to another element ‘ 
which is stable. The two elements ‘X’ and ‘Y’ were found to be in the ratio 1 : 7 in a sample of a given rock. The age of the rock is estimated to be
Text Solution
Verified by ExpertsThe correct answer is:
D
Initial number of atoms, N 0 0
Number of atoms after
time t N N 0 - N
As per question
or 
As 
where 
is the no. of halflives
or 
or 
years 
years
Hence, the age of rock is 60 years.
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