The disintegration of an isotope of sodium,$_{11}Na^{24} \to _{12}Mg^{24} + _{-1}e^0$,shown is due to

The value of one microcurie $=$ $.......$ disintegrations / second

In the decay sequence:
$^{238}_{92}U$ $\xrightarrow{- x_1} ^{234}_{90}Th$ $\xrightarrow{- x_2} ^{234}_{91}Pa$ $\xrightarrow{- x_3} ^{234}_{92}Z$ $\xrightarrow{- x_4} ^{230}_{90}Th$
$x_1, x_2, x_3$ and $x_4$ are particles/radiation emitted by the respective isotopes. The correct option$(s)$ is/are-
$(1)$ $Z$ is an isotope of uranium
$(2)$ $x_2$ is $\beta^{-}$
$(3)$ $x_1$ will deflect towards negatively charged plate
$(4)$ $x_3$ is $\gamma$-ray

Which of the following statements is correct?

Radioactive substances emit $\gamma$-rays,which are

In the reaction $_{93}Np^{239} \xrightarrow{} _{94}Pu^{239} + (?)$,the missing particle is