The half life of a radioactive isotope 'X ' is 20 years. It decays to another element 'Y ' 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:
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Question

The half life of a radioactive isotope 'X ' is 20 years. It decays to another element 'Y ' 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:

Options

G1 Physics · Accepted Answer

Step 1: Use N(t) = N₀ exp(−λt), A = λN and T₁/₂ = ln2/λ. Step 2: For two samples, write the decay law separately and equate the required activities/numbers. Final: C: 60 years.