1. Mixing two common occurring gases eg. N2, O2 does not require any input/output of energy unlike dissolving a solid in a solvent(endothermic eg. dissolving salt in water or exothermic eg. dissolving NaOH in water).
And your point is?
Whether the enthalpy of mixing is positive, negative or zero has nothing to do with whether or not we call the mixture a solution. If one of the components in the mixture makes up a large fraction, there's a fair chance that we'd call it a solution. If the minor component(s) are solid or gaseous, and the major component is liquid, we'd most probably call the mixture a solution.
2. There is no interaction between gas molecules of two different gases eg. He and O2. Unlike eg. hydrogen bonding in some liquid solutions eg. acetic aicd which has "unusual" higher boiling point.
Emphasis mine. Far from all liquids have hydrogen bonding between the molecules. What about liquid air? Is that a mixture of nitrogen, oxygen and argon, or is it a solution of oxygen and argon in nitrogen?
Let's look at some substances without hydrogen bonding between the molecules and extremely similar chemistry, like pure hydrocarbons. Let's take two gases, methane and ethane, two liquids, pentane and hexane, and two solids, octadecane and eicosane. Colloquially, we'd say that the mixtures of methane and hexane, or octadecane and hexane, are solutions, while the mixtures of methane and ethane, or pentane and hexane, or octadecane and eicosane, are mixtures. But there's really nothing fundamental which determines whether we call them "mixtures" or "solutions".
And what about the mixture of ethane and pentane? Both substances are liquid at at about -100 degrees C, so we'd probably call that a mixture of liquid ethane and liquid pentane. But at room temperature the ethane is gaseous and the pentane is liquid, and we'd probably call it a solution of ethane in pentane.
3. Gases do stratify by molecular weight in mesosphere or higher.
Not really. Take a look at the
NASA MSIS-E-90 Atmosphere Model page. The composition is pretty constant up to about 100km elevation, i.e. above the mesosphere and well into the thermosphere. And up there, the pressure and density are so low that we're in fact in a light vacuum. As Wikipedia says, the mean free path for a gas molecule in the thermosphere is about 1km. From there on, the fraction of He increases, but the ratios of the other gases (N2, O2 and Ar) doesn't show any "stratification by molecular weight".
4. Helium, the lightest molecule, escape from earth for good.
Because its low molecular mass gives it a high coefficient of diffusion, so it leads the race to the top, and a larger fraction of the He can reach escape velocity, also due to its low molecular mass. The atmosphere isn't a closed system at equilibrium, and there's also quite a bit of chemistry going on e.g. in the stratosphere where oxygen is continuously converted into ozone.
5. I am not talking about gas under pressure in a confined space(tank). It is about FREE moving one.
Pressure won't affect a gas' diffusion qualitatively, only quantitatively. The diffusion coefficient is roughly proportional to the pressure, but it isn't affected in any fundamental way.
And judging by some of the posts here, I'd guess there are two.
