When the transistor is used as an amplifier,
A. Emitter-base junctions must be reverse biased, and a collector-base junction must be forward biased.
B. Emitter-base junction must be forward biased, collector-base junction must be forward biased.
C. Emitter-base junction must be reverse biased, collector-base junction must be reverse biased.
D. Emitter-base junction must be forward biased, collector-base junction must be reverse biased.

Hint: In this question we have been asked to state that the conditions of the junctions when the transistor is used as an amplifier. To solve this question, we will define the condition for Emitter-base junction and collector base junction for an amplifier. We shall also discuss the working of a transistor as an amplifier. In doing, so we will select the appropriate statement.

Complete answer:
We know that for a transistor to act as an amplifier the, the transistor should be properly biased. A transistor will act as an amplifier by raising the strength of the input signal. A small change in input signal can lead to an appreciable change in the output when there is low resistance in the input circuit. When the transistor is biased to use as an amplifier, the input signals cause the emitter current to flow, which later contributes to the collector current. This current when flows through the load resistor, it results in a large voltage drop across. This shows that a transistor acts as an amplifier. The emitter base junction remains forward biased regardless of the polarity of the signal, when the DC voltage is applied.

So, the correct answer is “Option B”.

Note:
Since the emitter-base junction is heavily doped and moderate in size, it injects a large amount of charge carrier into the base. From this, the majority of charge carriers are collected at the collector. It is the output region from which the amplified current leaves through the transistor. Being that the collector will always attract more charge carriers.