$3.8$ days is the half-life period of a sample. After how many days, the sample will become $\frac{{1}}{{8}} \, th$ of the original substance

The half life of a radioactive sample undergoing $\alpha$ – decay is $1.4 \times 10^{17}$ s. If the number of nuclei in the sample is $2.0 \times 10^{21}$, the activity of the sample is nearly

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 $………………$

A radioactive sample has half-life of $5$ years. Probability of decay in $10$ years will be  ……..$\%$

Why radioactivity is considered a nuclear phenomenon ?