CONCEPT: Transistor: It is a semiconductor device that transfers a weak signal from a low resistance circuit to a high resistance circuit. The transistor is essentially a resistor that allows current to flow. The word transistor is a contraction of the current-transferring resistor. Transistors are commonly used in amplification, switching, and buffering signals or applied. There are two types of standard (bipolar junction) transistors, NPN and PNP. DIAGRAM FOR NPN AND PNP TRANSISTORS: ​Transistors have three terminals namely Emitter, Collector, and Base. Sr .No Emitter Collector Base 1. In a transistor, emitter supplies a large section of majority charge carriers. In a transistor, the section that collects the majority of the charge carrier supplied by the emitter is called a collector. The middle section of the transistor is known as the base. The collector-base junction is in reverse bias and offers higher resistance to the circuit. 2. The emitter is always forward biased with respect to the base so that it supplies the majority charge carrier to the base. The collector-base junction is always reverse biased. The base forms two circuits, the input circuit with the emitter, and the output circuit with the collector. The emitter-base is forward-biased and offers low resistance to the circuit. 3. The emitter of a transistor is heavily doped and moderate in size. The collector section of the transistor is moderately doped, but larger in size so that it can collect most of the charge carrier supplied by the emitter. The base of a transistor is lightly doped and very thin due to which it offers the majority charge carrier to the base. EXPLANATION: The key to the fabrication of a transistor is to make the middle layer, the base, as thin as possible without shorting the outside layers. It is customary to forward bias the emitter-base junction of a bipolar junction transistor as this increases the width of the depletion region whereas the base-collector junction is reverse biased. From the above discussion, it is clear that, The correct option is 3.