[jubba]

Are noble gas oxides acidic or basic? (or amphoteric or neutral)

I know this sounds like a stupid question because noble gase oxides aren't (very) stable but there has to be an answer. 

[DevaDevil]

Interesting question; I know heavier noble gases can indeed form oxides (like XeO₃), and indeed are usually not stable; XeO₃ and XeO₄ are pretty explosive.

A solution of XeO₃ will be acidic, because the compound XeO₄ will be formed in the following process:
XeO₃(aq) + H₂O ? H₂XeO₄ ? H⁺ + HXeO₄
A solution of XeO₄ however... probably will be basic, because of the reverse reaction (if this is a reversible reaction; not sure about that)

So the answer to the question pretty much depends on the different complexes the Noble gases form. These ones (of Xe) I know of, and the lighter noble gases really are inert. As for the rest... maybe someone else can fill in the gaps?

[jubba]

should the other heavier noble gases also have acidic oxides?
Since the oxygen will be electrophilic overal a noble gas oxide will be electrophilic making it a lewis acid. (is this right?)

[DevaDevil]

First of all let me clarify that in my previous post I assumed you were talking about the more common use of "acid" namely the Brønsted acid. And basically it isn't even a traditional acid in the way that it actually reacts with water, much in the same way that Sodium metal is a base because it reacts with water making the solution rise in pH.

Since I dont know the complexes of other noble gases, I cannot answer whether or not they will make a solution of them acidic or basic.

As for lewis acids; oxide (ions) usually are Lewis bases so that would make the "noble gas-cation" the acid, but in this case any electron transfer would be followed by an explosion, releasing the trapped oxide. The noble gas will not exist as cation. So... it's hard to speak about these instable materials in these terms.
(Lewis acid accepts the electron from the Lewis base, thus making a bond.)