In a radioactive decay chain reaction, ${ }_{90}^{230} Th$ nucleus decays into ${ }_{84}^{214} Po$ nucleus. The ratio of the number of $\alpha$ to number of $\beta^{-}$particles emitted in this process is. . . . .
$4$
$2$
$3$
$8$
The activity of a radioactive sample
The half-life of a radioactive substance is $3.6$ days. How much of $20\, mg$ of this radioactive substance will remain after $36$ days ............. $mg$
Radioactive substances do not emit
Match the nuclear processes given in column $I$ with the appropriate option$(s)$ in column $II$
column $I$ | column $II$ |
$(A.)$Nuclear fusion | $(P.)$ Absorption of thermal neutrons by ${ }_{92}^{213} U$ |
$(B.)$Fission in a nuclear reactor | $(Q.)$ ${ }_{27}^{60} Co$ nucleus |
$(C.)$ $\beta$-decay | $(R.)$ Energy production in stars via hydrogen conversion to helium |
$(D.)$ $\gamma$-ray emission | $(S.)$ Heavy water |
$(T.)$ Neutrino emission |
The half-life of ${ }^{198} {Au}$ is $3 \,days.$ If atomic weight of ${ }^{198} {Au}$ is $198\, {g} / {mol}$ then the activity of $2 \,{mg}$ of ${ }^{198} {Au}$ is ..... $\times 10^{12}\,disintegration/second$