Why is uranium-235 less stable than uranium-238?

The atomic number of uranium is 92. That makes U235 even-odd and U238 even-even. Even-odd nuclei are a little less bound per nucleon than even-even nuclei due to the pairing interactions. read more

Since uranium-238 has an even number of nucleons it is in a lower energy state (more compact) than if it had an odd number, like uranium-235. Thus uranium-235 is less stable. That is exactly why U-238 needs a fast neutron to fission but U-235 can fission with a slow neutron. read more

uranium 235 has disintegrating properties than uranium 238. it is unstable and have continuous and spontaneous chain reaction, which ends when uranium 235 finished. for more information refer book radioactive elements by R.K. JAIN. read more