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?

A. isotope division
B. ion acceleration
C. neutron absorption
D. neutron moderation

answer:

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.

hydrocarbons are organic compounds that contain only hydrogens and carbons. they can be saturated (those which contain only carbon-carbon single bonds) or unsaturated (those which contain carbon-carbon double or triple bonds) in nature. hydrocarbons can undergo several reactions like substitution, elimination etc.  

on substituting one or more hydrogen atoms in hydrocarbon it results in the formation of haloalkane. as the halogen atoms are large compared to the carbon and hydrogen atoms, due to which the molecular weight increases and the bond become polar because of presence electronegative halogen atom and results in the increase in boiling point of the haloalkane.

thus, the correct option is (b) that is the boiling point of the new compound increases on substituting a hydrogen atom with a halogen in a hydrocarbon.