On planet 3M4G6 in the subsystem Zeta-12, the atmosphere consists of a binary mixture of sewer gas (methane) and an unknown gas, called Esh-nugim Marookee Moo by the local mushfoot natives.
An extremely accurate spectral scan reveals that the mass fraction to mole fraction ratio for methane is 0.9341875 and the mole fraction of methane is 0.4281378. Determine the name of the unknown gas (in English).