$A$ radioactive isotope having a half-life period of $3 \ days$ was received after $12 \ days$. If $3 \ g$ of the isotope is left in the container,what would be the initial mass of the isotope?.......... $g$

$A$ freshly prepared radioactive source of half-life $2 \ hours$ emits radiations of intensity which is $64$ times the permissible safe level. The minimum time after which it would be possible to work safely with this source is ......... $hours$.

The Carbon-$14$ dating method is based on the fact that:

The amount of $_{53}I^{128}$ $(t_{1/2} = 25 \ min)$ remaining after $75 \ min$ is:

In a radioactive decay,a uranium atom transforms into a lead atom. If a rock sample from the moon contains an equal number of uranium and lead atoms,and the half-life $(t_{1/2})$ for uranium is $4.5 \times 10^9$ years,then the age of the rock will be:

The half-life of an isotope is $10 \ hrs$. How much will be left behind after $4 \ hrs$ in a $1 \ gm$ sample? (Assume the molar mass of the isotope is $1 \ g/mol$ for calculation purposes).