Which feature of nuclear fission reactions allows these reactions to take place in a chain reaction?

a) thermal energy is released and heats up the reactants.
b) more smaller atoms form that can undergo fission.
c) a larger atom is formed, which can then be split.
d) neutrons start the reaction and are released during it.

What does hund's rule state? a. an orbital can contain two electrons only if the electrons have opposite spins. b. an orbital can contain two electrons only if all other orbitals at that sublevel are empty. c. an orbital can contain two electrons only if the electrons have different energy levels. d. an orbital can contain two electrons only if all other orbitals in that sublevel contain at least one electron.