Q.Which is used as a moderator in a nuclear reactor?

Heavy water has the formula D2O.

Heavy water is chemically identical to ordinary water except that its hydrogen atoms are replaced by deuterium (2H, symbol D), the heavier stable isotope of hydrogen (mass number 2, containing 1 proton and 1 neutron). Its formula is therefore D2O, di …

D2O (heavy water) boils at about 101.4 degree C = 374.4 K, a little higher than ordinary water's 100 degree C = 373 K.

Heavy water, D2O, is chemically similar to ordinary water H2O but has deuterium (2H) in place of ordinary hydrogen (1H). Because deuterium is twice as massive as protium, the O-D bond is slightly stronger and shorter than the O-H bond, and hydrogen bonding between D2O molecules is marginally stronger. This raises D2O's boiling point slightly above that of ordinary water: D2O boils at about 101.4 degree C ( …

Heavy water is D2O.

Heavy water is water in which both ordinary hydrogen (protium, 1H) atoms are replaced by deuterium (2H or D), the heavier stable isotope of hydrogen. Its formula is D2O. It has a slightly higher density, boiling point and freezing point than ordinary water and is used as a neutron …

Heavy water (D2O) is used as a moderator in nuclear reactors because deuterium nuclei slow down fast neutrons by elastic collision while absorbing very few of them.

In a nuclear fission reactor, fast neutrons released by fission must be slowed to 'thermal' speeds so they can efficiently trigger further fission in fuel like U-235. A moderator does this by elastic collisions with light nuclei. D2O (heavy water) is an effective moderator because deuterium (mass close to a neutron) slows neutrons efficiently while having a very low neutron-capture cross-section. (Note: the paper's own option (b) prints 'V-235', which looks like a typesetting slip for the reactor fuel …

'Use of heavy water' matches with 'In atomic reactor', since D2O (heavy water, made from the hydrogen isotope deuterium) is used as a neutron moderator in nuclear reactors.

Heavy water, D2O, is made using deuterium (2H), an isotope of hydrogen with one extra neutron. Because deuterium nuclei slow down fast neutrons efficiently through elastic collisions while absorbing very few of them, D2O is used as a …

Heavy water is D₂O — water in which the hydrogen atoms are replaced by the heavier hydrogen isotope deuterium (D).

Ordinary water is H₂O. Deuterium (²₁H, symbol D) is an isotope of hydrogen with one proton and one neutron, roughly twice the mass of protium (¹₁H). Water formed from deuterium and oxygen, D₂O, is therefore called 'heavy water' — it has a higher density and higher boiling point than ordinary water an …