The number of beta particles emitted by a radioactive substance is...

Let the radioactive substance be ${ }_{\mathrm{Z}}^{\mathrm{A}} \mathrm{X}$ Radioactive transition is given by { }_{\mathrm{Z}}^{$\mathrm{A}$} $\mathrm{X} \stackrel{-\alpha}{\longrightarrow}{ }_{\mathrm{Z}-2}^{\mathrm{A}-4} \mathrm{X} \stackrel{-2 \beta}{\longrightarrow}{ }_{\mathrm{A}-4} \mathrm{X}$The atoms of element having same atomic number but different mass numbers are called isotopes. So, ${ }_Z^A X$ and ${ }_Z^{A-4} X$ are isotopes.