A sample of diatomic gas A has three times the mass of an equal volume of gas B under the same conditions. What is the ratio of the atomic mass of A to that of B?
Let's say that the formula of Gas A is
Avogadro's Law tells us that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.
Thus, if Gas A has three times the mass of an equal volume of Gas B, a molecule of Gas A must have three times the mass of an atom of Gas B.
But a molecule of Gas A contains two atoms of
Hence each atom of