$A$ radioactive nucleus decays as follows. If the atomic number of $X$ is $72$ and the mass number is $180$,what are the mass number and atomic number of $X_4$?
$X \xrightarrow{\alpha} X_1 \xrightarrow{\beta} X_2 \xrightarrow{\alpha} X_3 \xrightarrow{\gamma} X_4$

In the uranium radioactive series,the initial nucleus is $_{92}U^{238}$ and the final nucleus is $_{82}Pb^{206}$. When the uranium nucleus decays to lead,the number of $\alpha$-particles emitted will be

When an element ${}_{90}^{232}Th$ decays into ${}_{82}^{208}Pb$,the number of $\alpha$ and $\beta^{-}$ particles emitted respectively are

Pauli suggested the emission of neutrino during $\beta^{+}$ decay to explain:

In the given nuclear reaction,$A, B, C, D, E$ represent:
$_{92}U^{238} \xrightarrow{\alpha} _{B}Th^{A} \xrightarrow{\beta} _{D}Pa^{C} \xrightarrow{E} _{92}U^{234}$

$A$ radio nuclide $A_1$ with decay constant $\lambda_1$ transforms into a radio nuclide $A_2$ with decay constant $\lambda_2$. If at the initial moment the preparation contained only the radio nuclide $A_1$,then the time interval after which the activity of the radio nuclide $A_2$ reaches its maximum value is: