A nucleus of mass M+△m is at rest and decays into two daughter nuclei of equal mass M2 each. Speed of light is c.
The binding energy per nucleon for the parent nucleus is E1 and that for the daughter nuclei is E2. Then
E2>E1
The reaction is X→2Y
X→mass is M+△m
Y→mass is M2
Now, this is energetically feasible only if the daughter nucleus has a higher binding energy than the parent, so E2>E1.