$A$ radioactive element with half-life $6.5 \ hr$ has $48 \times 10^{19}$ atoms. Number of atoms left after $26 \ hr$ is:

The ratio of $\frac{{}^{14}C}{{}^{12}C}$ in a piece of wood is $\frac{1}{8}$ part that of the atmosphere. If the half-life of ${}^{14}C$ is $5730 \text{ years}$,the age of the wood sample is $.....$ years.

The half-life of an isotope is $10 \ hrs$. How much will be left behind after $4 \ hrs$ in a $1 \ gm$ sample? (Assume the molar mass of the isotope is $1 \ g/mol$ for calculation purposes).

$87.5\%$ decomposition of a radioactive substance completes in $3$ hours. What is the half-life of that substance?

The half-life for radioactive decay of $^{14}C$ is $5730 \ years$. An archaeological artifact containing wood had only $80\%$ of the $^{14}C$ found in a living tree. The age of the sample is ....... $years$.

$A$ radioactive substance takes $20 \, \text{min}$ to decay $25 \%$. How many minutes will it take to decay $75 \%$?