When Iodine-131 emits a β particle will produce Xe-131
Radioactivity is the process of unstable isotopes to stable isotopes by decay, by emitting certain particles,
So for reaction Iodine-131 :
[tex]\tt _{53}^{131}I\rightarrow _{-1}^0\beta +_{54}^{131}Xe[/tex]
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