Question

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

• A. 150 years
• B. 200 years
• C. 250 years
• D. 100 years

Answer 1

Answer: (B)

$X\to Y$
$X:Y=1:15$
A.P. $=\frac{1}{16}=\frac{1}{2^n}$
No. of half life $n=4$
$t=n{T}_{1/2}=4\times 50=200yr$