The way I see it, there are no word tricks, the answer is not hidden in the narrative.
If I understand where awuh is going with the problem, it is simply this. There is one pardon, for the prisoner who is in cell A, B or C at daybreak. It could be a daily reprieve, given the OP, but I digress. The warden knows which cell's occupant gets the reprieve. Pardon, I mean. This language stuff is tricky.
Anyway, The warden tells prisoner 1, who is in cell A, that the king's decision means that the dude in C goes to the gallows tomorrow. Now that he knows this, should he stay in A or choose cell B instead?