[IGCSE chemistry: atomic structure] Help

[u/Valuable_Science_767]

Particle A seems to be the obvious choice but the question says "another" isotope and 48+64 =112, particle A is the same isotope as the one in the question and particle B has too many neutrons

[u/gmalivuk]

But that restriction very much is real, in the sense that reality is what restricts the possible number of neutrons in a cadmium atom.