Concept:The most useful mode of a BJT is the active mode, where the emitter-base junction is forward-biased and the base-collector junction is reverse-biased.
Explanation:In the active mode, the emitter-base junction is forward-biased, which allows charge carriers to be injected from the emitter into the base.
The base-collector junction is reverse-biased, which collects these carriers and produces the amplified output current.
This forward-reverse biasing combination gives the BJT its current amplification property, making it suitable for amplifier and switching applications.
In the cut-off mode, both junctions are reverse-biased, so the transistor is completely off and no current flows.
In the saturation mode, both junctions are forward-biased, so the transistor is fully on with maximum current flow.
In the reverse-active mode, the emitter-base junction is reverse-biased and the base-collector junction is forward-biased, but this mode is rarely used in practical circuits.
Therefore, the active mode with forward-biased emitter-base and reverse-biased base-collector is the most useful biasing condition.
Answer:Option B: Active Mode: Emitter-base junction is forward-biased, and base-collector junction is reverse-biased.