Based on the information in the graph why is energy released during the fission of a uranium (u) nucleus?

D

Explanation:

Fission is the break of the nuclei of an unstable atom, releasing heat in the process. By the graph shown, U-238 has less average binding energy per nucleon comparing to U-235. Because it has less binding energy, it is more difficult for it to react (it has less energy to release), so it is more stable than U-235.

The product of its fission is the U-235, an isotope that has a small mass than the uranium. So the mass that is lost during fission is converted to the binding energy in the isotope, making it slightly higher (the difference of mass is only 3 amu).