The decay constant for a radioactive nuclide is $1.5 \times 10^{-5} s ^{-1}$. Atomic of the substance is $60\,g$ mole $^{-1},\left( N _{ A }=6 \times 10^{23}\right)$. The activity of $1.0\,\mu g$ of the substance is $…….\,\times 10^{10}\,Bq$

A sample of radioactive material $A$, that has an activity of $10\, mCi\, (1\, Ci = 3.7 \times 10^{10}\, decays/s)$, has twice the number of nuclei as another sample of different radioactive material $B$ which has an activity of $20\, mCi$. The correct choices for half-lives of $A$ and $B$ would then be respectively

In a sample of radioactive material, what percentage of the initial number of active nuclei will decay during one mean life ………. $\%$

A radio-isotope has a half- life of $5$ years. The fraction of the atoms of this material that would decay in $15$ years will be

If a radioactive element having half-life of $30\,min$ is undergoing beta decay, the fraction of radioactive element remains undecayed after $90\,min$. will be :