$N$ atoms of a radioactive element emit $n$ number of $\alpha$-particles per second. Mean life of the element in seconds, is

The half life period of radioactive element ${x}$ is same as the mean life time of another radioactive element $y.$ Initially they have the same number of atoms. Then:

A radioactive sample $\mathrm{S} 1$ having an activity $5 \mu \mathrm{Ci}$ has twice the number of nuclei as another sample $\mathrm{S} 2$ which has an activity of $10 \mu \mathrm{Ci}$. The half lives of $\mathrm{S} 1$ and $\mathrm{S} 2$ can be

The half life of a radioactive element which has only $\frac{1}{{32}}$ of its original mass left after a lapse of $60\, days$ is ........$days$

Radioactive element decays to form a stable nuclide, then the rate of decay of reactant is

Unit of radioactivity is Rutherford. Its value is