A p-n junction diode is forward-biased when its p-side (anode) is connected to a higher potential and its n-side (cathode) is connected to a lower potential ($V_p > V_n$). Conversely, if the n-side is at a higher potential than the p-side, it is reverse-biased. To identify the forward-biased circuit from the given options, one must evaluate the voltage at both terminals of the diode and choose the one where the potential at the p-side is strictly greater than the potential at the n-side.