$99 \%$ of a radioactive element will decay between

If $20\, gm$ of a radioactive substance due to radioactive decay reduces to $10 \,gm$ in $4 \,minutes,$ then in what time $80\, gm $ of the same substance will reduce to $10 \,gm$

Two radioactive materials $X_1$ and $X_2$ have decay constant $5\lambda$ and $\lambda$ respectively intially they have the saame number of nuclei, then the ratio of the number of nuclei of $X_1$ to that $X_2$ will be $\frac{1}{e}$ after a time

A sample of a radioactive nucleus $A$ disintegrates to another radioactive nucleus $B$, which in turn disintegrates to some other stable nucleus $C.$ Plot of a graph showing the variation of number of atoms of nucleus $B$ vesus time is :

(Assume that at ${t}=0$, there are no ${B}$ atoms in the sample)

The decay constant of a radio isotope is $\lambda$. If  $A_1$ and $A_2$ are its activities at times $t_1$ and $t_2$  respectively, the number of nuclei which have decayed during the time $(t_1 - t_2)$ 

A radioactive sample has half-life of $5$ years. Probability of decay in $10$ years will be  ........$\%$