The average molecular weight of air is 29, and the sum of the relative atomic weights of each atom in the chemical formula is the relative molecular weight, which is represented by the symbol Mr. As long as the gas is less than the average molecular weight of air, the balloon can float.

Extended data

To calculate the average relative molecular weight of a molecule, we only need to use the periodic table of elements to find out the sum of the atomic weights of each atom of this substance. To calculate the relative molecular weight, we can use the method of calculating the average relative molecular weight when the topic does not specify the atomic weight of the atom of this molecule. When it represents the atomic weight of an element of this molecule, we use this number. Of course, the answer at this time is generally different from the average relative molecular weight.

Hydrogen is the least dense gas known in the world, and its density is only114 of that of air, that is, at 0℃ and a standard atmospheric pressure, its density is 0.0899 g/L. ..

Helium is a colorless and odorless gas at room temperature and atmospheric pressure. Its volume content in dry air is 5.24× 10-6. It is the substance with the lowest critical temperature found by human beings. Dark yellow when discharged at low voltage.