Mark of preference by individual about name for element (5)

I believe the answer is:

xenon

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'for element' is the definition.
(xenon is a kind of element)

I cannot understand how the rest of the clue works.

(Other definitions for xenon that I've seen before include "Gaseous element, Xe" , "member of nobility?" , "One of the noble set" , "Inert gas, Xe" , "Inert 18" .)

I've seen this clue in The Times and The Sunday Times.

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