what particle is emitted in the radioactive decay 23892u→23490th

the correct equation should be

²³⁸U → ^234Th + ⁴He

 From the above equation we can we clearly that the atomic mass decrease by 4 while the number of nuclear charge or atomic number decreases by two, this types of decay  is an alpha emission,  the particle emitted is an alpha particle, that is a helium nuclei, therefore in  the decay of Uranium-238 to Torium-234, an alpha particle is emitted.