Out of the following, which one is not emitted by a natural radioactive substance?

$A$ nucleus with mass number $220$ is initially at rest. It emits an $\alpha$-particle. If the $Q$-value of the reaction is $5.5 \, MeV$,then the kinetic energy of the $\alpha$-particle will be .......... $MeV$.

$A$ radioactive nucleus emits a beta particle. The parent and daughter nuclei are

$A$ 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 $..................$

Explain the conservation of linear momentum for the radioactive decay of a radium nucleus.

$U^{238}$ decays into $Th^{234}$ by the emission of an $\alpha$-particle. There follows a chain of further radioactive decays,either by $\alpha$-decay or by $\beta$-decay. Eventually,a stable nuclide is reached,and after that,no further radioactive decay is possible. Which of the following stable nuclides is the end product of the $U^{238}$ radioactive decay chain?