The element with a mass number of 19 could be fluorine, which is a halogen and a gas, but not a noble gas.
Fluorine is a gas with a mass number 19.
The element with a mass of 30 and is a noble gas, other than neon, is krypton (Kr). With an atomic number of 36, krypton has 36 protons in its nucleus and typically has 44 neutrons in its most common isotope, giving it an atomic mass near 84.
Helium
Helium with an atomic mass of 4.00260
Noble gases belong to group 0 and can be found on the extreme right column of the periodic table of elements. The heaviest noble gas would be radon, whose atomic mass is still uncertain. The element which appears below radon in the column, ununoctium, has not been confirmed as a noble gas.
This gas is likely to be fluorine (F), which has a mass number of 19. Fluorine is a highly reactive, pale yellow gas that is part of the halogen group on the periodic table. It is commonly found in compounds rather than in its pure elemental form due to its high reactivity.
The noble gas with 48 neutrons and a mass of less than 100 is Krypton. It has an atomic number of 36, which means it has 36 protons in its nucleus. The total mass of Krypton is slightly less than 100 atomic mass units.
Atomic mass increases from top to bottom and left to right on the periodic table. In each row, the noble gasses have the highest atomic mass. As you travel down that column, also called a group or family, the noble gasses increase in atomic mass. The naturally occurring noble gas with the highest atomic mass is Radon (Rn; atomic mass = 211.4 amu). In 2002, the unstable element Ununoctium was synthesized, and although it is a member of group 18, it was later determined to be a solid at room temperature, so it is not classified as a noble gas.
The fluorine-19 isotope.
The gas has molecules that are single atoms, as do the noble gases.
No, it is a noble gas
No halogen gas has a mass of under 15 atomic mass units. The closest is fluorine, at 19.0 atomic mass units.