Concept:Heavy water is named because it contains deuterium, a heavier isotope of hydrogen, instead of the common protium isotope.Explanation:Normal water (H₂O) uses protium, which has only one proton and no neutron. Heavy water (D₂O) uses deuterium, which has one proton and one neutron. This extra neutron makes deuterium about twice as heavy as protium, giving heavy water its name. Heavy water is used in nuclear reactors and has a slightly higher density, but these are not the reasons for its name. The core reason is the replacement of protium with deuterium.Answer:Option A – it uses Deuterium, a heavier isotope of hydrogen, rather than Protium.