In complete sentence we can say that- All the noble gases except radon occur in the atmosphere. They are chemically unreactive. They have their valence cell orbitals completely filled. Since non metal are the element which accepts electron to complete their octet while noble gases already have a complete octet.so noble gas is a non metal
First of all, not everyone considers noble gases to be non-metals but those who do argue that since many PHYSICAL properties of noble gases resemble that of non-metals, they should be included in non-metals.
because its tendency to lose electrons or gain electrons is 0 and is a gas.