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The half life of a radioactive isotope 'X' is 50 years. It decays to another element 'Y' which is stable. The two elements 'X' and 'Y' were found to be in the ratio of 1 : 15 in a sample of a given rock. The age of the rock was estimated to be
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- 150 years
- 200 years
- 250 years
- 100 years
Correct Option: B
Let number of atoms in X = Nx
Number of atoms in Y = Ny
By question
| = | ||||
| N0 | 15 |
| ∴ Part of Nx = | (Nx + Ny) | |
| 16 |
| = | (Nx + Ny) | |
| 24 |
So, total 4 half lives are passed, so, age of rock is 4 × 50 = 200 years
