Answer the following question:
Write the process of ${\beta }^{-}$ decay. How can radioactive nuclei emit $\beta -$particles even though they do not contain them ? Why do all electrons emitted during $\beta -$decay not have the same energy ?

In ${\beta }^{-}$decay, the mass number A remains unchanged but the atomic number Z of the nucleus goes up by $1.$ A common example of ${\beta }^{-}$decay is
${}_{15}^{32}P{\to }^{32}16S+e^{-}+\stackrel{-}{v}$
A neutron of nucleus decays into a proton, an electron and an antineutrino. It is this electron which is emitted as ${\beta }^{-}$ particles.
${}_0^{1}n{\to }_1^{1}p{+}_{-1}^{0}e+\stackrel{-}{v}$
In $\beta$-decay, particles like antineutrinos are also emitted along with electrons. The available energy is shared by electrons and antineutrinos in all proportions. That is why all electrons emitted during ${\beta }^{-}$decay not have the same energy.