Draw a graph showing the variation of decay rate with number of active nuclei. 

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 …… $sec$

Half life of a radio-active substance is $20\, minutes$. The time between $20\%$ and $80\%$ decay will be ……….. $minutes$

In a radioactive reaction $_{92}{X^{232}}{ \to _{82}}{Y^{204}}$, the number of $\alpha – $ particles emitted is

The decay constant $\lambda $ of the radioactive sample is the probability of decay of an atom in unit time, then