The half-life of a radioactive isotope is $3 \ hr$. The value of its disintegration constant is: (in $hr^{-1}$)

The decay of a radioactive element follows first-order kinetics. As a result:

$A$ radioactive element decays at such a rate that after $15 \ min$ only $1/10$ of the original amount is left. How many more minutes will be needed when only $1/100$ of the original amount will be left? .......... $\min$

What is the order of a radioactive decay reaction?

Assuming $1 \, \mu g$ of trace radioactive element $X$ with a half-life of $30 \ years$ is absorbed by a growing tree. The amount of $X$ remaining in the tree after $100 \ years$ is $n \times 10^{-1} \, \mu g$. Find the value of $n$. $[Given : \ln 10 = 2.303 ; \log 2 = 0.30]$

The half-life of $^{14}C$ is about $.........$ $years$.