why would "you all find the key!" be wrong? I thought trovate is you all and trova is just singular you
I don't think it's technically wrong, but it would be an unusual usage, especially in the imperative. Pronouns are usually implied from verb context in italian, and in the imperative (when one is giving an order) even more so.
I tried "Trova la chiave!" (singular) and it was accepted. So both trovate and trova are correct.
Does this work equally well for musical keys as for lock keys?
E se non ci riusciamo? Cosa faremo allora?
Why is "you find the key" wrong. This construction is common English when speaking to more than one person. It is equivalent to saying "find the key."
You find the ley should be marked correct.