$A$ wood piece is $11460$ years old. What is the fraction of $^{14}C$ activity left in the piece? (Half-life period of $^{14}C$ is $5730$ years)

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 of a radioactive isotope is $3 \ hours$. If the initial mass of the isotope is $256 \ g$,how much mass in $g$ will remain after $18 \ hours$ (in $.0$)?

$A$ 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 ....... $\min$

The disintegration constant of radium with a half-life of $1600 \ years$ is:

Initial mass of a radioactive element is $40 \ g$. How many grams of it would be left after $24 \ years$,if its half-life period is $8 \ years$?