The half-life of $_6C^{14}$ if its decay constant $k$ or $\lambda$ is $2.31 \times 10^{-4} \ yr^{-1}$ is:

$A$ wood specimen from an archeological site shows a $_6^{14}C$ activity of $5.0 \ counts/min/gm$ of carbon. If a freshly cut wood gives $15 \ counts/min/gm$ of carbon,what is the age of the specimen? (Given: $t_{1/2}$ for $_6^{14}C$ is $5000 \ years$)

What is the percentage of a radioactive element decayed after $20 \ s$ if its half-life is $4 \ s$?

An element has a half-life of $1600 \ years$. The fraction of the mass left after $6400 \ years$ will be:

The half-life period of ${}_{53}I^{125}$ is $60$ days. The radioactivity after $180$ days will be (in $\%$)

If the quantity of a radioactive element is doubled,then its rate of disintegration per unit time will be