Diode's asymmetric I-V curve identifies it uniquely

Steps:

• Examine the graph for linearity: straight line indicates ohmic behavior like resistors.
• Check symmetry: forward and reverse currents differ greatly in diodes.
• Note non-linearity: current rises sharply after threshold in forward bias for diodes.
• Compare to options: only diode shows rectification, not seen in conductors or resistors.

Why D is correct:

• Semiconductor diodes follow the diode equation $I = I_s (e^{V/(nV_T)} - 1)$, yielding exponential forward current and near-zero reverse current.

Why the others are wrong:

• A. Filament lamp: curve bends upward due to heating, but symmetric and ohmic at low voltages.
• B. Metal conductor at constant temperature: straight line through origin per Ohm's law $V = IR$.
• C. Resistor: linear straight line through origin, constant resistance.

Final answer: D