Which of the following defines the process that decreases the number of slow moving neutrons to prevent the chain reaction in a nuclear reactor from going too fast?

The correction option is D.
Neutron moderation is a  process through which the speed of fast neutrons is reduced in nuclear engineering; it results in turning neutrons to thermal neutrons which are capable of sustaining a nuclear chain reaction. 

There is one s orbital, and there are three p orbitals, five d orbitals, and seven f orbitals. thus, the answer is b. do not confuse the number of orbitals in a subshell with the number of electrons the subshell can hold. each orbital can hold two electrons, so the capacity of an nf subshell is 14 electrons.