Radon is radioactive.its nucleus isnt stable.then y is it a noble gas?

Nobility refers to reactivity, not radioactivity.

radioactive means it's atomic weight is higher than 85.noble gas means the gas which doesn't make any chemical process with any other elimen in normal circmstancis.radon needs heavy pressure and heat to get stable using lead.so it is a noble gas.

an element requires only its outermost shell of electrons to be stable , it has to be no relation with nucleus cuz protons can be increased in any stable element but electrons can't be in stable element

It still has 8 electrons in it outer electron shell. This makes it non-reactive.

bcoz its valency orbital has 8 electrons. so its octet is complete.

just to answer your first question, it is a noble gas because it does not react chemically with other elements. ;-D Chemical activity and nuclear activity are totally different.

as it has 8 electrons in the outer most shell it is a noble gas ther is no connection between the radio active chareater of a matereil and the noble gas poperty it is determined by the number of electons in the outer most shell only hope ur doubt is cleard

You should not get confused with the Chemical reaction and nuclear reaction. Chemical reaction depends on the chemical environment, i. e. the no of electrons in the outer most shell. However nuclear reaction does not depend on chemical environment, rather on the nutron to proton ratio (n/p). So nuclear disintegration will continue unless it will become stable. So chemically Radon is non reavtive or noble but it disintegrates and loses its electronic structure. But till it has the electronic structure like that of inert gases in its native state it is unreactive.

Essentially chemically inert, but radioactive, radon is the heaviest noble gas and one of the heaviest gases at room temperature. (The heaviest known gas is Uranium hexafluoride, UF6.) At standard temperature and pressure radon is a colorless gas but when it is cooled below its freezing point it has a brilliant phosphorescence which turns yellow as the temperature is lowered and orange-red at the temperature air liquefies. Natural radon concentrations in Earth's atmosphere are so low that radon-rich water in contact with the atmosphere will continually lose radon by volatilization. Hence, ground water has a higher concentration of Rn-222 than surface water. Likewise, the saturated zone of a soil frequently has a higher radon content than the unsaturated zone due to diffusional losses to the atmosphere.