The proposal here seemed to go down well, and in the spirit of 'just trying this and seeing if it works', here we go with Topic Challenge I.
I've picked these as they're generally broad topics which are under-represented here on chem.SE at present. In future (if this works...) it would be good if the community could decide what the challenge tags were, possibly by answering on the initial proposal with suggestions (and an explanation and rationale for why you want that tag).
In terms of what questions you can ask, anything goes as long as it's on-topic and broadly related to one of the chosen tags. Feel free to ask one/several questions on either/both, but remember that this is about encouraging quality questions, so lets not just add to the 'close' queue!
For any questions I think need or deserve it, I'll add (or try and coordinate) some bounties and in two weeks time I'll post an answer here with the stats on how many questions have been asked on these tags, how many answers those questions have had and anything else notable.
Remember to tag the question with the relevant tag (there is no specific topic challenge tag, and theres no need to try and make one).
If you have any questions, you can ask them here or bring it up in chat.
(Largely copied from GraphicDesign.SE with some modifications/additions).