At any instant,the ratio of the amount of two radioactive substances is $2 : 1$. If their half-lives are $12$ hours and $16$ hours respectively,what will be the ratio of the substances after two days?

The activity of a radioactive sample is $1.6 \, curie$ and its half-life is $2.5 \, days$. Its activity after $10 \, days$ will be .......... $curie$.

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

The number of undecayed nuclei $N$ in a sample of radioactive material as a function of time $t$ is shown in the figure. Which of the following graphs correctly shows the relationship between $N$ and the activity $A$?

Two radioactive substances $A$ and $B$ have the same number of initial nuclei. If the half-lives of $A$ and $B$ are $1.5 \ days$ and $4.5 \ days$ respectively,then the ratio of the number of nuclei remaining in $A$ and $B$ after $9 \ days$ is

Two radioactive isotopes $P$ and $Q$ have half-lives $10 \text{ minutes}$ and $15 \text{ minutes}$ respectively. Freshly prepared samples of each isotope initially contain the same number of atoms. After $30 \text{ minutes}$,the ratio $\frac{\text{number of atoms of } P}{\text{number of atoms of } Q}$ will be