Half-life of a radioactive substance which disintegrates by $75\%$ in $60 \ min$ will be ......... $min$.

Gadolinium-$153$,which is used to detect osteoporosis (porous bones),has a half-life of $242$ days. Which value is closest to the percentage of $Gd-153$ left in a patient's system after $2$ years? .......... $\%$

The Carbon-$14$ dating method is based on the fact that:

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

The radioisotope,tritium $({}_1^3H)$ has a half-life of $12.3 \ years$. If the initial amount of tritium is $32 \ mg$,how many milligrams of it would remain after $49.2 \ years$?

$A$ radioactive isotope decays at such a rate that after $192 \ min$ only $1/16$ of the original amount remains. The half-life of the radioactive isotope is ....... $\min$