The half-life of a radioactive substance is $48$ hours. How much time will it take to disintegrate to its $\frac{1}{{16}} \,th$ part ............$hour$

A fraction $f_1$ of a radioactive sample decays in one mean life, and a fraction $f_2$ decays in one half-life.

In saloons, there is always a characteristics smell due to the ammonia-based chemicals used in hair dyes and other products. Assume the initial concentration of ammonia molecules to be $1000 \,molecules/ m ^3$. Due to air ventilation, the number of molecules leaving in one minute is one tenth of the molecules present at the start of that minute. How long will it take for the concentration of ammonia molecules to reach $1 \,molecule / m ^3$ ?

A radioactive nucleus decays by two different processes. The half life for the first process is $10\, s$ and that for the second is $100 s$. the effective half life of the nucleus is close to$.....sec$

Half life of radioactive element depends upon

$N$ atoms of a radioactive element emit $n$ alpha particles per second. The half life of the element is