why can it be said that the noble gases are reactive and how?

what is the mechanism involed in the sp3 hybridisation

the outer shell

valence electrons are the ones involved in chemical bonds

Aside from Helium :)

Why aside from Helium (all noble gases or just helium in general?)?

The reason is that He, (and I am pretty sure Ne) don't undergo any chemical reactions. Therefore you can't say their valence electrons are involved in reactions.

There are many known fluorides and oxides of Xenon (e.g. XeF2, XeF4, XeF6, XeO2, XeO2F2, ...). There are also a few chemical reactions that Krypton undergoes, maybe Argon too.

hmm... i thought all noble gases didn't react. So how do they react through electrons? Do they bond covelently, ionically or what?

The bonds are covalent. To put it in easy words: Flourine wants a bond so badly that it will even attack Xenon which is not interested in a bond for itself. The resulting molecule has a lower energy then Xenon atoms and Florine molecules seperately.

The mechanism is promotion: Xenon has unoccupied 5d orbitals. Their energy is just a little bit higher than their highest occupied orbitals (5p). So Xenon puts its electrons up into 5d (and needs a little bit of energy for that). Then it has unpaired electrons that it uses to form bonds with. The bonding energy then compensates the promotion energy. It only works with very electronegative elements though, for Xe you have only F, O, and Cl compounds. For Kr, Ar probably just F.

Promotion happens in any molecule where the valence of the central atom exceeds 8, e.g. polyatomic ions like nitrate, sulfate, chlorate, ...
and also molecules like BrF3, ICl3, IF7, ...

This theory also explains why it might never be possible to have He and Ne compounds: Because of the fact that there are no d-orbitals, promotion would have to go to the next s-orbital. The energy needed for that could not be compensated by any bonding energy.

:lol: @ 'promotional energy'

It explains it well, even if it is codswallop :lol:

I believe a few (transient?) Ne compound has been created.
HeBeO is also possible, theoretically (Structure and existance predicted in 1986)

It's all abot Molecular orbitals, and Ionisation Potentials.
And even that's codswallop :lol:

I think Ar too.