If $8.0 \ g$ of a radioactive substance has a half-life of $10 \ hrs.$,the half-life of $2.0 \ g$ of the same substance is .......... $hr$.

If the half-life of a certain radioactive nucleus is $1000 \ s,$ the disintegration constant is

The decay of $_{92}U^{235}$ is a reaction of .......... order.

What is the half-life (in $\text{min}$) of a radioactive substance if $75\%$ of a given amount of the substance disintegrates in $30 \, \text{min}$?

The half-life period $t_{1/2}$ of a radioactive element is $N$ years. The period of its complete decay is

$A$ freshly prepared radioactive element has a half-life of $2 \ hr$. It emits radiation whose intensity is $64$ times the permissible safe level. The minimum time after which it would be possible to work with this sample is .......... $hr$.