A radio-isotope has a half- life of $5$ years. The fraction of the atoms of this material that would decay in $15$ years will be
$1/8$
$2/3$
$7/8$
$5/8$
$99\%$ of a radioactive element will decay between
$1\, Curie $ is equal to
In Fig. $X$ represents time and $Y$ represent activity of a radioactive sample. Then the activity of sample, varies with time according to the curve
The activity of a radioactive material is $2.56 \times 10^{-3} \,Ci$. If the half life of the material is $5$ days, after how many days the activity will become $2 \times 10^{-5} \,Ci$ ?
$A$ and $B$ are two radioactive substances whose half lives are $1$ and $2$ years respectively. Initially $10\, gm$ of $A$ and $1\, gm$ of $B$ is taken. The time (approximate) after which they will have same quantity remaining is ........... $years$