Question

A radioactive isotope having a half life of $3$ days was received after $12$ days. It was found that there were $3gm$ of the isotope in the container. The initial mass of the isotope when packed was:

• A. $48gm$
• B. $36gm$
• C. $24gm$
• D. $12gm$

Answer 1

The correct option is A $48gm$

Let initial sample be $x$.

After 12 days ( 4 half lives ) $\frac{x}{16}$ will be left.

Given $\frac{x}{16}=3g$

$⟹x=48g$