What is the order of a radioactive decay reaction?

What is the half-life period of a nucleus in $days$ if at the end of $4.2$ $days$,$N = 0.798 \ N_0$?

The half-life period of radioactive decay of ${}^{14}C$ is $5730 \ years$. An archaeological artifact contains $80\%$ of ${}^{14}C$ as compared to a living tree. Calculate the age of the sample in $years$.

The amount of $_{53}I^{128}$ $(t_{1/2} = 25 \ min)$ remaining after $75 \ min$ is:

$A$ first-order nuclear reaction is half-completed in $45 \ minutes$. How long does it take for $99.9\%$ of the reaction to be completed in $hours$?

During a nuclear explosion,one of the products is $^{90}Sr$ with a half-life of $28.1 \ years$. If $1 \ \mu g$ of $^{90}Sr$ was absorbed in the bones of a newly born baby instead of calcium,how much of it will remain after $10 \ years$ and $60 \ years$ if it is not lost metabolically?