which of the following represents correct order of conductivity in solids ?

Options

A. `K_("metals")gt gt K_("insulators") lt K_("semiconductors")`
B. `K_("metals")lt lt K_("insulators") lt K_("semiconductors")`
C. `K_("metals"), K_("semiconductors") gt K_("insulators")="zero"`
D. `K_("metals")lt K_("semiconductors") gt K_("insulators")ne"zero"`

Answer

To determine the correct order of conductivity in solids, we need to analyze the conductivity of different types of solids: metals, insulators, and semiconductors.

### Step-by-Step Solution:

1. **Understanding Conductivity**:
- Conductivity (denoted as \( k \)) is a measure of a material's ability to conduct electric current. It is influenced by the availability of charge carriers (like electrons) and their mobility.

2. **Conductivity in Metals**:
- Metals have a high density of free electrons that can move easily throughout the material. This high mobility of electrons results in high conductivity.
- The conductivity of metals typically ranges from \( 10^4 \) to \( 10^7 \, \text{S/m} \) (Siemens per meter).

3. **Conductivity in Insulators**:
- Insulators have very few free charge carriers. The energy gap between the valence band and the conduction band is large, preventing electrons from moving freely.
- As a result, insulators have very low conductivity, typically ranging from \( 10^{-20} \) to \( 10^{-10} \, \text{S/m} \).

4. **Conductivity in Semiconductors**:
- Semiconductors have a moderate number of charge carriers. Their conductivity can vary significantly with temperature and the presence of impurities (doping).
- The conductivity of semiconductors generally ranges from \( 10^{-6} \) to \( 10^4 \, \text{S/m} \).

5. **Comparing Conductivities**:
- Based on the above analysis, we can summarize the conductivity of each type of solid:
- Metals: Highest conductivity (\( k \) is highest)
- Semiconductors: Moderate conductivity (\( k \) is in the middle)
- Insulators: Lowest conductivity (\( k \) is lowest)

6. **Correct Order of Conductivity**:
- Therefore, the correct order of conductivity from highest to lowest is:
\[ \text{Metal} > \text{Semiconductor} > \text{Insulator} \]
- This can be expressed as:
\[ k_{\text{metal}} > k_{\text{semiconductor}} > k_{\text{insulator}} \]

### Conclusion:
The correct answer is **A**: Metal > Semiconductor > Insulator.