The most common isotope is protium with mass no.1 and atomic mass 1.007822 and the protium nucleus is a proton. The other isotope of hydrogen is deuterium with mass no 2 and atomic mass 2.0140 it is called heavy hydrogen. It is known as by chemical formulas by the symbol D. The deuterium nucleus or ion is also called the deuteron. It is formed with proton and neutron. In atmospheric h... https://www.expertsmind.com/chemistry/hydrogen-isotopes-properties-assignment-help.aspx