In a transistor,

Options

A. the emiiter has the least concentration of impurity
B. the collector has the least concentration of impurity
C. the base has the least concentration of impurity
D. all the three region have equal concentration of impurity

Answer

To solve the question about the concentration of impurities in different regions of a transistor, we will analyze the structure and doping levels of an NPN transistor step by step.

### Step-by-Step Solution:

1. **Identify the Structure of the NPN Transistor**:
- An NPN transistor consists of three regions: the Emitter (N), the Base (P), and the Collector (N).
- The arrangement is Emitter-Base-Collector.

2. **Understand the Doping Levels**:
- The Emitter is heavily doped with N-type material, which means it has a high concentration of electrons (majority carriers).
- The Base is lightly doped with P-type material, which means it has a low concentration of holes (majority carriers).
- The Collector is moderately doped with N-type material, which means it has a moderate concentration of electrons.

3. **Comparing the Doping Concentrations**:
- The Emitter has the highest concentration of impurities due to heavy doping.
- The Base has the lowest concentration of impurities because it is lightly doped.
- The Collector has a moderate concentration of impurities, more than the Base but less than the Emitter.

4. **Conclusion**:
- Based on the doping levels, the correct statement regarding the concentration of impurities is that the Base has the least concentration of impurities compared to the Emitter and Collector.

5. **Select the Correct Option**:
- Therefore, the correct option is: "The base has the least concentration of impurity."