$^{14}C$ has a half-life of $5760 \ years$. $100 \ mg$ of a sample containing $^{14}C$ is reduced to $25 \ mg$ in ......... $years$.

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

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 half-life period of a radioactive element is $30 \ min$. One sixteenth of the original quantity of the element will remain unchanged after ........... $min$.

The half-life of $^{60}Co$ is $7 \ years$. If $1 \ g$ of it decays,the amount of the substance remaining after $28 \ years$ is (in $g$)

$\frac{15}{16}$-th of a radioactive sample decays in $40$ days. The half-life of the sample is ...... days.