The decay constant of a radioactive element is $0.01$ per second. Its half life period is .......$sec$

A radioactive reaction is $_{92}{U^{238}}{ \to _{82}}P{b^{206}}$. How many $\alpha $ and $\beta $  particles are emitted

Write the definition and unit of decay constant. 

The half-life of a radioactive nucleus is $5$ years, The fraction of the original sample that would decay in $15$ years is

The rate of disintegration of fixed quantity of a radioactive element can be increased by

A radio-active material is reduced to $1 / 8$ of its original amount in $3$ days. If $8 \times 10^{-3}\,kg$ of the material is left after $5$ days. The initial amount of the material is $.......\,g$