When a potential difference is applied across, the current passing through

Options

A. an insulator at 0 K is zero
B. a semiconductor at 0K is zero
C. a metal at 0 K is finite
D. a `p-n ` dipole at 300 K is finite, if it is reverse biased.

Explanation

To solve the question regarding the behavior of current in different materials at specific temperatures and conditions, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Option A: Insulator at Zero Kelvin**
- An insulator is a material that does not allow current to flow through it under normal conditions. At absolute zero (0 Kelvin), the thermal energy is minimal, and the electrons in an insulator are tightly bound to their atoms. Therefore, no current can flow.
- **Conclusion:** The current is zero in an insulator at 0 Kelvin. Thus, **Option A is correct.**

2. **Option B: Semiconductor at Zero Kelvin**
- A semiconductor has properties between those of insulators and conductors. At 0 Kelvin, a semiconductor behaves like an insulator because all the charge carriers (electrons and holes) are frozen in place and cannot move. Hence, no current can flow.
- **Conclusion:** The current is zero in a semiconductor at 0 Kelvin. Thus, **Option B is correct.**

3. **Option C: Metal at Zero Kelvin**
- Metals typically conduct electricity due to the presence of free electrons. At 0 Kelvin, metals become superconductors, which means they can conduct electricity without resistance. Theoretically, this results in an infinite current since the resistance drops to zero.
- **Conclusion:** The current in a metal at 0 Kelvin is infinite. Thus, **Option C is incorrect.**

4. **Option D: P-N Diode at 300 Kelvin in Reverse Bias**
- A P-N diode allows current to flow in one direction (forward bias) but blocks it in the reverse direction. When reverse-biased, only a very small leakage current flows due to minority charge carriers (electrons in the p-type region and holes in the n-type region).
- **Conclusion:** A very small current flows in a reverse-biased P-N diode at 300 Kelvin. Thus, **Option D is correct.**

### Final Summary of Options:
- **Option A:** Correct (Current is zero)
- **Option B:** Correct (Current is zero)
- **Option C:** Incorrect (Current is infinite)
- **Option D:** Correct (Very small current flows)