Consider the following two statements:
$A.$ The energy spectrum of $\alpha-$ particles emitted in radioactive decay is discrete.
$B.$ The energy spectrum of $\beta-$ particles emitted in radioactive decay is continuous.

The radioactive decay of uranium into thorium is expressed by the equation $_{92}^{238}U \to _{90}^{234}Th + X,$ where $X$ is

Assertion: ${}_{Z}{X^{A}}$ undergoes $2\alpha$-decays,$2\beta$-decays,and $2\gamma$-decays,and the daughter product is ${}_{Z-2}{X^{A-8}}$.
Reason: In $\alpha$-decays,the mass number decreases by $4$ and the atomic number decreases by $2$. In $\beta$-decays,the mass number remains unchanged,but the atomic number increases by $1$.

$A$ 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

If a nucleus $P$ converts into a nucleus $Q$ by the decay of one alpha particle and two $\beta^{-}$ particles, then the nuclei $P$ and $Q$ are

Beta rays emitted by a radioactive material are