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

A radioactive sample decays by $\beta$  -emission. In first two seconds $‘n’$  $\beta$ -particles are emitted and in next $2\ seconds$ , $‘0.25n’$ $\beta$ -particles are emitted. The half life of radioactive nuclei is ...... $sec$

After $280$ days, the activity of a radioactive sample is $6000\, dps$. The activity reduces to $3000\, dps$ after another $140\, days$. The initial activity of the sample in dps is

A freshly prepared radioactive sample of half- life $1$ hour emits radiations that are $128$ times as intense as the permissible safe limit. The minimum time after which this sample can be safely used is .........$hours$

What fraction of a radioactive material will get disintegrated in a period of two half-lives

Following statements related to radioactivity are given below

$(A)$ Radioactivity is a random and spontaneous process and is dependent on physical and chemical conditions.

$(B)$ The number of un-decayed nuclei in the radioactive sample decays exponentially with time.

$(C)$ Slope of the graph of $\log _{e}$ (no. of undecayed nuclei) $Vs$. time represents the reciprocal of mean life time $(\tau)$.

$(D)$ Product of decay constant ( $\lambda$ ) and half-life time $\left(T_{1 / 2}\right)$ is not constant.

Choose the most appropriate answer from the options given below