Water used as moderator in nuclear reactor is called (a) heavy water(b) hard water(c) nuclear water(d) critical water

In a nuclear reactor, a moderator is used to slow down the neutrons produced during the nuclear fission process, enabling the chain reaction to continue efficiently. Water is one of the common materials used as a moderator.

Heavy water (D₂O): This is water in which the hydrogen atoms are replaced with deuterium (an isotope of hydrogen). It is a common moderator used in nuclear reactors because deuterium has a lower tendency to absorb neutrons than ordinary hydrogen, allowing more neutrons to sustain the chain reaction.

Hard water: Refers to water that has high concentrations of dissolved minerals, such as calcium and magnesium. It has no role in nuclear reactions.

Nuclear water: This is not a scientifically recognized term and does not refer to anything specific.

Critical water: This refers to water at critical temperature and pressure conditions, usually in the context of fluid dynamics or thermodynamics, but it's not used as a term for a moderator.

Answer:
The correct option is (a) heavy water because heavy water is used as a moderator in some nuclear reactors.