After $3$ hours, only $0.25 \,mg$ of a pure radioactive material is left. If initial mass was $2 \,mg$ then the half life of the substance is ...... $hr$
$1.5$
$1$
$0.5$
$2$
A radioactive sample is undergoing $\alpha$ decay. At any time $t_{1}$, its activity is $A$ and another time $t _{2}$, the activity is $\frac{ A }{5}$. What is the average life time for the sample?
A radioactive substance emits
Radioactivity was discovered by
What can be found from decay curve ?
A radioactive element ${ }_{92}^{242} X$ emits two $\alpha$-particles, one electron and two positrons. The product nucleus is represented by ${ }_{ P }^{234} Y$. The value of $P$ is $..................$