U 92238 has 92 protons and 238 nucleons.It decays by emitting an alpha particle and becomes

Let the daughter nucleus X ZA. So, reaction can be shown asU 92238→X ZA+He 24From conservation of atomic mass238 = A + 4⇒A = 234From conservation of atomic number92 = Z + 2⇒Z=90So, the resultant nucleus is X 90234, i.e., Th 90234.