Which is a characteristic of nuclear fusion but not nuclear fission?
a. releases large amounts of energy
b. is the energy source of stars
c. is used in electric power plants
d. requires little energy to occur

 Nuclear fusion is the energy source of stars.

This is the option thats characterisitic of nuclear fusion and not nuclear fission.

Explanation:

Both nuclear fusion and nuclear fission releases large amount of energy.

Nuclear fission is a process of splitting a large radioactive nuclei into lighter nuclie and the energy released is used to generate electricity.

Nuclear fission requires little energy to occur.

Nuclear fusion is the process when two lighter nuclei under high Temperature and pressure combine to form a heavier nuclei to release large amount of energy.

And this process generally happens only in stars.

Nuclear fusion is the energy source of stars.

Nuclear fusion cannot be done on earth as earth cannot make this high Temperature and pressure,hence it cannot be used to generate electricity.  

Hence,nuclear fusion is the energy source of stars is the only characterisitic of nuclear fusion among these four options given here.  

definition

                    entropy is a measure of the randomness or the extent of disorder of a chemical process.

                      enthalpy is a measure of the heat change of a reaction occurring at a constant pressure.

measurement units:

                        entropy is measured in joule per kelvin (jk⁻¹)   whereas enthalpy is measured in joule per mole (jmol⁻¹)

requirements:

                            entropy has no requirements or limits, and its change is measured by the division between the heat change of the chemical process and the temperature.

                              in contrast, enthalpy can only be related to the heat change of the reaction under standard conditions.