D2O, commonly known as heavy water, is a form of water where the hydrogen atoms are replaced with deuterium, a heavier isotope of hydrogen. This gives D2O a higher molecular weight than regular water (H2O). Heavy water is used in various scientific applications, including nuclear reactors, where it acts as a neutron moderator, slowing down neutrons to sustain nuclear fission. In addition to its use in nuclear technology, D2O is also utilized in certain types of spectroscopy and biochemical research. Its unique properties allow scientists to trace chemical reactions and study molecular structures more effectively. Heavy water is not toxic but should be handled with care due to its different physical properties.