The atomic sizes of noble gases are by far the largest in their respective periods-why?

The atomicity of noble gases is

The atomic sizes of the noble gases are greater than that of the halogen. Why?

Why noble gases are called rare gases ?

Statement I : Noble gases have highest ionization energies in their respective periods. Statement II : The ns-np of outermost shell of noble gases is completely filled.

Why noble gases are inert or inactive ?

Assertion : Noble gases have highest ionisation enthalpies in their respective periods. Reason : Noble gases have stable closed shell electronic configuration.

Assertion : Noble gases have highest ionisation enthalpies in their respective periods. Reason : Noble gases have stable closed shell electronic configuration.