The decay constant of a radioactive element is $0.01 \ s^{-1}$. Its half-life period is ....... $s$.

$A$ sample initially contains $10^{20}$ radioactive atoms. The number of $\alpha$-particles emitted in the third year is $0.3$ times the number of $\alpha$-particles emitted in the second year. How many $\alpha$-particles are emitted in the first year?

The half-life of a radioactive substance is $48$ hours. How much time will it take to disintegrate to its $\frac{1}{16}$th part?

The half-life period of radium is $1600$ years. The fraction of a sample of radium that would remain after $6400$ years is

$A$ fraction $f_1$ of a radioactive sample decays in one mean life,and a fraction $f_2$ decays in one half-life.

Half-life period of a sample is $15$ years. How long will it take to decay $96.875\%$ of the sample?