No halogen gas has a mass of under 15 atomic mass units. The closest is fluorine, at 19.0 atomic mass units.
Oxygen - Atomic Mass: 15.9994.
Sodium is a metal element. Atomic mass number of it is 23.
There are many isotopes that have a mass number of 40. Calcium 20 has a mass number of 40 but so does potassium 21 and Argon 22. Calcium twenty however is probably the one you want as it is more common then the other isotopes listed.
Calcium is a metal element. Atomic mass of it is 40.
Neon
Neon.
Neon
There is no such noble gas with an atomic mass of 30. The mass of neon is 20 and the mass of the next noble gas, argon, is 40
The gas with atomic mass of 16 and has 8 neutrons is oxygen.
Helium with an atomic mass of 4.00260
Calcium: Atomic # is 20, & the atomic mass is 40.078 amu.
Radon has atomic mass of 222. There is isotope of Radon with mass number 226. Radon is a Nobel gas.
Argon is a non meta element. Atomic mass of it is 40.
Neon is a non metal element. Atomic mass of it is 20.
Neon is a non metal element. Atomic mass of it is 20.
No halogen gas has a mass of under 15 atomic mass units. The closest is fluorine, at 19.0 atomic mass units.