Avogadro's Number: `6.022xx10^(23)`
In a thermal neutron-inducted fission process, `.^(235)U` reacts with a neturon and breaks up into energetic fragmants and (normally) `2-3` new neutrons.
We consider one single fission event: `235U+n rarr .^(137)Te+X+2n`
Identify the fragment X.

Answer

`.^(97)Zr`