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My Chemistry teacher is at it again. Today, I cautiously approached his office and stopped in the doorway instead of walking right in - and it's a good job I did. There he was again - bent over on the carpet, arranging his Periodic Table element flashcards in some new and completely unscientific manner, taking up almost the entire floor.

Under his breath, he muttered, "Gargh, I haven't left enough room at the top..." and in his hands he held two flashcards whose faces I couldn't quite see. At this point he became suddenly aware of my presence, stood up abruptly, and concealed these two flashcards behind his back.

I opened my mouth to speak but he beat me to it. "You have another question about the classwork, don't you?" He smiled. "Tell you what - you can ask your question, but only if you can first tell me which two elements I am holding in my hand..."

TASK: Considering the arrangement of flashcards below, which two elements are missing from the pattern? Where should they both be placed in relation to the other cards on the floor?

Flashcard arrangement

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  • $\begingroup$ Did you create this puzzle? $\endgroup$
    – Tony Ennis
    Jun 2, 2022 at 19:12
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    $\begingroup$ Fun fact (ROT13): Va Pnanqn, gurer'f bayl bar cebivapr be greevgbel (bhg bs guvegrra) jubfr cbfgny nooerivngvba vf funerq jvgu na ryrzrag. So that might not make for a good puzzle. $\endgroup$ Jun 2, 2022 at 19:16
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    $\begingroup$ @TonyEnnis Yes I did, and the one linked in the preamble. Each flashcard is made of three cells in MS Excel, which I then snipped and overlaid in their corresponding positions over the relevant map (which I deleted before posting here). Two long lists had to be consulted to make sure I caught them all! $\endgroup$
    – Stiv
    Jun 2, 2022 at 19:25

2 Answers 2

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Your teacher is holding cards for the elements

PA and HS! (Protactinium and Hassium)

Reasoning: The cards are arranged in the order of the

British Postal Codes, as shown here:
map

Near the top of the map we see spaces for PA and HS, where there wasn't quite enough room on the original image.

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  • $\begingroup$ Aw, looks like you beat me to it while I was making the image. $\endgroup$
    – Deusovi
    Jun 1, 2022 at 0:14
  • $\begingroup$ Well spotted :) Checkmark awarded on timestamp grounds since both answers are correct and include a diagram - couldn't really ask for much more! $\endgroup$
    – Stiv
    Jun 1, 2022 at 19:17
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It seems like the two missing elements are

Hassium (Hs) and Protactinium (Pa)...

or rather,

the Outer Hebrides and Paisley!

These are the postal codes of the UK, arranged as shown in the following image:

UK map with corresponding regions highlighted

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