Should I Dip This In Acetone

I also agree, this one should be left alone.

Leave it as is.

I don't consider a dip in acetone cleaning. I consider it preserving.

Do real just_carl's many remarks about getting good, clean acetone that hasn't sat around...

Otherwise, he'll come around here and whoop us whipper-snappers.

It would probably shatter into a lot of pieces since liquid nitrogen boils at -196 °C or -320 °F, which is rather cold.

madspec

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After a 5 minute immersion in liquid nitrogen @-197.3C (-323F) the nickel was unfazed. I threw it at a concrete floor a few times with no effect. I then gave it a good whack with a pipe wrench which resulted in the nasty rim ding but the planchet held up to the short term exposure. I might try repeating this sometime with an overnight immersion and dropping onto concrete from 20+ feet.

Superglue.

Seriously though, if it's got green on it, best to kill it now and preserve the coin. Just soak for a few minutes without any rubbing to kill it.

Superglue? That would never work. It is to brittle and if dropped from the top of a building the glue wouldn't hold.
Use a wire type welder, blast furnace or arc welder

In reality leave well enough alone. Or as they said in the very, very old days, let sleeping dogs lie.

I ended up using epoxy to put it back together, it is very permanent.

no more ugly coin.

error

Back to the coin. What would happen to a nickel dipped in liquid nitrogen and then dropped onto a concrete floor?

The main thing here is how you dipped it. For example if you used your fingers to dip it, I would think there would be more of a problem with your fingers than with the coin. Next you would have to consider dry or wet concrete. If recently poured, the Nickel may well sink. Also, you never mentioned the height from which the coin is to be dropped. Now if from a buildings roof, you could hit someone on the head and end up with a law suit and never get your Nickel back.