Are there any discovered bodies in the outer solar system that are known to be probably made mostly of frozen hydrogen,helium or rare gas ice instead of being mostly made of frozen water and methane with a bit of hydrocarbon "dirt"? And what is the exact average composition of the outer (KB) solar system bodies and comets?

Does hydrogen or helium freeze solid outside of a laboratory?

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"The beauty of that discussion of averages is that you don't have to be an expert in Apollo or in photography in order to see where this time study "analysis" breaks down. You just have to be, well...not an idiot." -JayUtah

The melting point of Hydrogen at atmospheric pressure is 14.01 K, for comparision the current temperature on Eris is around 18 K, so in outer KB the temperature is low enough to freeze it.

Helium cannot freeze solid at atmospheric pressure or in vacuum at all, but I wonder; could it be the component of some KBOs interiors where it is frozen by high pressure along with lower temperature?

Noble gases freezing points (at 1 atm. unless specified otherwise);

Helium (at 2.5 MPa): 0.95 K
Neon: 24.56 K
Argon: 83.80 K
Krypton: 115.79 K
Xenon: 161.4 K
Radon: 202 K

Also, another question, can be frozen chunks of these gases floating in the interstellar space near or in nebulas where solar system is being born?

Huh?Absolutely no other answers?

Compression tends to heat stuff (it's the gas law), so I would not expect a lower temperature in the center of a KBO.

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Optimism does not change the laws of physics. (T'Pol)
A good scientist has freed himself of concepts and keeps his mind open to what is. (Dao De Jing 27)
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Martin ( http://www.geocities.com/DrMartinV )

However compression heat will not remain infinitely.And you have pressure of cca 2.5 MPa fairly shallow under the surface, you don't need planetary core pressures to freeze helium, 2.5 MPa is just cca 25 atmospheres.Even Venus's atmosphere has much more pressure.