$A$ radioactive substance contains $10000$ nuclei and its half-life period is $20$ days. The number of nuclei present at the end of $10$ days is

Which sample contains a greater number of nuclei: a $5.00 \mu Ci$ sample of $^{240}Pu$ (half-life $6560 \ y$) or a $4.45 \mu Ci$ sample of $^{243}Am$ (half-life $7370 \ y$)?

The half-life of radon is $3.8 \ days$. Three-fourths of a radon sample decays in ............ $days$.

$A$ radioactive nucleus with a decay constant $\lambda = 0.5/s$ is being produced at a constant rate of $P = 100\, nuclei/s$. If at $t = 0$ there were no nuclei,the time when there are $N = 50\, nuclei$ is:

$x$ fraction of a radioactive sample decays in $t$ time. What fraction will decay in $2t$ time?

$A$ solution containing active cobalt ${}_{27}^{60}Co$ having activity of $0.8\,\mu Ci$ and decay constant $\lambda$ is injected into an animal's body. If $1\,cm^3$ of blood is drawn from the animal's body after $10\,hrs$ of injection,the activity found is $300\,decays$ per minute. What is the total volume of blood in the animal's body in litres? (Given: $1\,Ci = 3.7 \times 10^{10}$ decays per second and at $t = 10\,hrs$,$e^{-\lambda t} = 0.84$)