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The half life of 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
Options
(a) 150 years
(b) 200 years
(c) 250 years
(d) 100 years
Correct Answer:
200 years
Explanation:
Let no. of atoms in X = Nₛ, No. of atoms in Y = Nₜ
By eq. Nₛ / Nₜ = 1/15
Part of Nₛ = 1/16 (Nₛ + Nₜ) = 1/2⁴ (Nₛ + Nₜ)
So, total 4 half lives are passed, so, age of rock is 4 x 50 = 200 years.
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Subject: Physics
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