Assertion: Group 18 elements do not combine with any other elements.
Reason: All the elements of group 18 have a stable configuration.
Both assertion and reason are true and the reason is the correct explanation of the assertion.
The members of the group 18 have eight electrons in their valence shell (except helium which has two electrons). Their electronic configuration is considered to be stable, since they are chemically unreactive, which means they don't combine with other elements to form compounds. The elements are also known as inert gases.