Let us consider there will be current (I≠0) flowing through the two ends of a P-N junction joined by a wire. This should generate heat at metal ohmic contacts (the metal used to connect p-n junction and the wire). This heat must be supplied by the p-n junction since there is no other external excitation applied. The p-n junction, therefore, would have to cool off. Clearly, under thermal equilibrium the simultaneous heating of metal ohmic contacts and cooling of the p-n junction is impossible and we conclude that I꞊0. Therefore, the correct answer is option A.