Which one of the following isotopes of Uranium is used as fissile material in nuclear thermal power plants?

Uranium-235 is the fissile isotope used in nuclear thermal power plants.

Uranium-234 is a trace isotope with no role as reactor fuel.

Uranium-238 is fertile rather than fissile, absorbing neutrons instead of splitting easily.

Uranium-239 is a short-lived isotope formed transiently, not a fuel.

Only uranium-235 readily sustains a fission chain reaction with slow neutrons.

Natural uranium is enriched to raise its uranium-235 content for reactor use.