The unit of the decay constant for radioactive disintegration is:

$_{11}Na^{24}$ has a half-life of $15 \ h$. On heating,its half-life will:

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 $8 \ years$?

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

The half-life of a radioisotope is $4 \ h$. If the initial mass of the isotope was $200 \ g$,the mass remaining after $24 \ h$ undecayed is ........... $g$.

The half-life of a radioactive substance is $120$ days. After $480$ days,the amount of $4 \ g$ of the substance remaining will be: (in $g$)