In Fig. $X$ represents time and $Y$ represent activity of a radioactive sample. Then the activity of sample, varies with time according to the curve

The activity of a sample is $64 × 10^{-5}\, Ci.$ Its half-life is $3\, days$. The activity will become $5 × 10^{-6}\, Ci$ after ………$days$

The half-life of $^{238} _{92} U$ undergoing $\alpha$ -decay is $4.5 \times 10^{9}$ $years$. What is the activity of $1\; g$ sample of $^{238} _{92} U$?

The half-life of radium is about $1600$ years. Of $100\, g$ of radium existing now, $25\, g$ will remain unchanged after ………. $years$

Explain the $\alpha -$ decay process and give its appropriate example