Question

The noble gases are essentially non-reactive. This is because A. They are all rare gases. B. Their inner electron shells are all full. C. Their valence electron shells are all full. D. They are in need of more valence electrons.

Answer 1

The noble gases are essentially non-reactive. This is because
their valence electron shells are all full. ( C ). They have no
interest in finding more electrons, or in sharing what they have.

Answer 2

C. Their valence electrons shells are full.  All noble gasses have their outer most Orbitals filled with eight electrons, filling the octet rule. This makes the element more stable.