Heavy water is so called because it

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contains a number of salts as in sea water

is the mercury contaminated water

is saline water used in hospitals

contains the heavier isotope of hydrogen in water

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Answer is Wrong!

This question was previously asked in

UPSC CAPF – 2011

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The correct option is D. Heavy water, chemically represented as D₂O, contains deuterium, which is an isotope of hydrogen. Unlike the common hydrogen atom (protium, ¹H) which has only a proton, deuterium (²H or D) has a proton and a neutron, making it approximately twice as heavy as protium. Therefore, water molecules formed with deuterium (heavy water) are heavier than those formed with protium (ordinary water, H₂O).

The question asks for the reason why heavy water is called “heavy”. It relates to its chemical composition and the presence of a heavier isotope of hydrogen.

Heavy water is primarily used as a neutron moderator in certain types of nuclear reactors (pressurized heavy water reactors – PHWRs) because deuterium has a lower neutron capture cross-section than protium, allowing for the use of unenriched uranium as fuel.

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