Question: A good diode checked by a multimeter should indicate :

Step 1 (Governing Principle): [0.5 Mark]
The fundamental property of a $p\text{-}n$ junction diode is its unidirectional current flow. According to the NCERT physics curriculum, a diode acts as a conductor in forward bias (where the $p$-region is connected to the positive terminal and $n$-region to the negative terminal) and as an insulator in reverse bias (where the $p$-region is connected to the negative terminal and $n$-region to the positive terminal).

Step 2 (Logical Deduction): [0.25 Mark]
By Ohm's Law, $R = \frac{V}{I}$.

• In forward bias, the depletion layer narrows, allowing a large current ($I$) to flow, resulting in a low resistance ($R$).
• In reverse bias, the depletion layer widens, restricting current flow to a negligible leakage current, resulting in a high resistance ($R$).

Step 3 (Final Concluded Answer): [0.25 Mark]
Comparing the deduction with the given options, a functional diode must show low resistance in forward bias and high resistance in reverse bias. Therefore, the correct option is (A).

💡 EL10 Concept Insight: Think of a diode like a one-way turnstile at a park; it lets you walk through easily in one direction (forward bias), but it locks up and stops you completely if you try to go the other way (reverse bias).