In the following equation representing $\beta^{-}$ decay,the number of neutrons in the nucleus $X$ is ${ }_{83}^{210} Bi \longrightarrow X + { }_{-1}^{0} e + \bar{\nu}$

When a nucleus with atomic number $Z$ and mass number $A$ undergoes a radioactive decay process:

$A$ radioactive nucleus ${}_{Z}^{A}X$ undergoes spontaneous decay in the sequence ${}_{Z}^{A}X \rightarrow {}_{Z-1}B \rightarrow {}_{Z-3}C \rightarrow {}_{Z-2}D$,where $Z$ is the atomic number of element $X$. The possible decay particles in the sequence are:

Which spectrum is continuous?

Give a brief explanation about radioactivity.

${}^{238}U$ has $92$ protons and $238$ nucleons. It decays by emitting an alpha particle and becomes: