An element used for radioactive carbon dating for more than $5600$ years 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 $7370 \ y$)?

What percentage of original radioactive atoms is left after five half-lives (in $\%$)?

$A$ radioactive sample disintegrates via two independent decay processes having half-lives $T_{1/2}^{(1)}$ and $T_{1/2}^{(2)}$ respectively. The effective half-life $T_{1/2}$ of the nuclei is

The graph between the instantaneous concentration $(N)$ of a radioactive element and time $(t)$ is:

$A$ radioactive element $ThA$ $(_{84}Po^{216})$ can undergo $\alpha$ and $\beta$ types of disintegrations with half-lives $T_1$ and $T_2$ respectively. Then the effective half-life of $ThA$ is: