The half life $(T)$ and the disintegration constant $(\lambda )$ of a radioactive substance are related as

Draw a graph of the time $t$ versus the number of undecay nucleus in a radioactive sample and write its characteristics. 

Half-life of a radioactive substance is $20\,minute$ . The time between $20\%$ and $80\%$ decay will be ......... $min$

The graph in figure shows how the count-rate $A$ of a radioactive source as measured by a Geiger counter varies with time $t.$ The relationship between $A$ and $t$ is : $($ Assume $ln\,\, 12 = 2.6)$

The activity of a radioactive sample is measured as $9750$ counts per minute at $t = 0$ and as $975$ counts per minute at $t = 5$ minutes. The decay constant is approximately ............ per minute

Activities of three radioactive substances $A , B$ and $C$ are represented by the curves $A, B$ and $C,$ in the figure. Then their half-lives $T _{\frac{1}{2}}( A ): T _{\frac{1}{2}}( B ): T _{\frac{1}{2}}( C )$ are in the ratio