Uranium-238 decays into Thorium-232 by emitting

A Hydrogen nucleus

B beta particles

C gamma rays

D alpha particles

D alpha particles

Explanation:

Radioactive U-238 will decay into Thorium - 232 by emitting alpha particles in the process of nuclear fission.

Nuclear fission is the radioactive decay process in which a heavy nucleus spontaneously disintegrates into two lighter ones and several other particles with a large release of energy.

U-238 → Th-232 + alpha particles + 2 neutrons + energy

This way the mass and atomic numbers are conserved;