Pt's inner element? (3)

I believe the answer is:

tin

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'element?' is the definition.
(tin is a kind of element)

I don't understand the rest of the clue.

(Other definitions for tin that I've seen before include "1 down, symbol Sn" , "Money" , "Silver-white metal, used to make cans" , "Canister" , "Cornish metal?" .)

I've seen this clue in the Sydney Morning Herald.

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