Question

A radio active isotope having a half life of $3$ days was received after $9$ days. It was found that there was only $4gms$ of the isotope in the container. The initial weight of the isotope when packed was:

• A. $8gms$
• B. $64gms$
• C. $48gms$
• D. $32gms$

Answer 1

The correct option is D $32gms$

Half life $=3days$
Let initial amount in the container $=x$
Fraction of amount left after 3 half lives,
$(\frac{1}{2}{)}^3=\frac{1}{8}$

So, $\frac{1}{8}$ of $x=4gms$
$\Rightarrow x=32gms$