Tritium has a half-life of $12.5\; y$ undergoing beta decay. What fraction of a sample of pure tritium will remain undecayed after $25\; y$?

$A$ radioactive material of half-life $T$ was kept in a nuclear reactor at two different instants. The quantity kept the second time was twice that kept the first time. If their present activities are $A_1$ (first) and $A_2$ (second) respectively,then their age difference is equal to:

If the half-life of a radioactive element is $3 \ hours$,what fraction of its initial activity remains after $9 \ hours$?

$A$ radioactive substance decays to $\left(\frac{1}{16}\right)^{th}$ of its initial activity in $80\, days$. The half-life of the radioactive substance expressed in days is ... .

The fraction of the initial number of radioactive nuclei which remain undecayed after half of a half-life of the radioactive sample is

The activity of a radioactive sample is measured as $N_0$ counts per minute at time $t=0$,and $\frac{N_0}{e}$ counts per minute at time $t=3$ minutes. The activity reduces to half its value in time (in minutes) is: