GENERAL KNOWLEDGE

Detailed explanation-1: -Moderator is required in a Nuclear reactor to slow down the neutrons produced during the fission reaction so that the chain reaction can be sustained. Heavy Water is an excellent moderator due to its high moderating ratio and low absorption cross section for neutrons.

Detailed explanation-2: -Heavy water i.e., D2O slows down the speed of neutrons in nuclear reactors.

Detailed explanation-3: -The correct answer is to Slow down the speed of neutrons.

Detailed explanation-4: -The moderator is a material intentionally placed in a nuclear reactor core to slow neutrons down from their initial fast speeds. Adding a moderator makes it much easier to attain a nuclear chain reaction. In common water-cooled nuclear reactors, the moderator is the same thing as the coolant: water.