Group 18 elements are the noble gases (He, Ne, Ar, Kr, Xe, Rn). They are generally unreactive because they have a full outer shell of electrons.

Therefore, they do not readily form oxides, and the oxides they do form are not basic.

Here's why:

* Oxides are formed by reaction with oxygen. Noble gases are very unreactive, and most don't readily form oxides.

* Basic oxides are formed by metals, which tend to lose electrons. Noble gases have a very stable electron configuration, making them reluctant to lose electrons.

While some heavier noble gases like Xenon (Xe) can form oxides under extreme conditions, these oxides are more likely to be neutral or acidic rather than basic.

In summary, the oxides of Group 18 elements are not considered to be basic.