The half-life of radon is $3.8 \ days$. Three-fourths of a radon sample decays in ............ $days$.

The activity of a radioactive sample falls from $700 \; s^{-1}$ to $500 \; s^{-1}$ in $30 \; min$. Its half-life is close to ......... $min$.

If $20 \, g$ of a radioactive substance reduces to $10 \, g$ due to radioactive decay in $4 \, minutes$, then in what time will $80 \, g$ of the same substance reduce to $10 \, g$?

$A$ radioactive element initially has $4 \times 10^{16}$ active nuclei. If its half-life is $10 \ days$,find the number of nuclei that have decayed in $30 \ days$.

$A$ radioactive substance has a half-life of $60\, minutes$. After $3\, hours$,the fraction of atoms that have decayed would be ......... $\%$

In one average lifetime of a radioactive nucleus,