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

(a) 80 years

(b) 100 years

(c) 40 years

(d) 60 years

Answer 1

The correct option is (d) 60 years.

Explanation:

As per question

n = t/T_1/2 or t = nT₁₂ = 3 x 20 yeras = 60 years.

Hence, the age of rock is 60 years.