* Alpha Decay: Alpha decay involves the emission of an alpha particle, which is a helium nucleus (²⁴He or ⁴₂He).

* Uranium-238: This isotope has 92 protons (atomic number 92) and 146 neutrons (238 - 92 = 146).

The Decay Process:

When uranium-238 undergoes alpha decay:

* Atomic Number: The atomic number decreases by 2 (92 - 2 = 90).

* Mass Number: The mass number decreases by 4 (238 - 4 = 234).

The Resulting Nuclide:

The resulting nuclide has an atomic number of 90 and a mass number of 234. This corresponds to Thorium-234 (²³⁴Th).

Therefore, the nuclide produced when uranium-238 decays by alpha emission is Thorium-234.