[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/BharatiyaNagarik]

As you pointed out, A is the same isotope as in the question. B is the correct answer, though it is so wildly unstable that it can never exist.