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napoleonponapa1) what is in your mind?
2) What is on your mind? #2 is by far the more common, but #1 is also correct.
#2 usually anticipates that you wish to ask something or say something, and it invites you to proceed.
#1 is similar to "What could you possibly be thinking of?", implying that you're showing some sign of wrongheadedness. "What's