Assertion: If there is some gap between the conduction band and the valence band, electrons in the valence band all remain bound and no free electrons are available in the conduction band. Then the material is an insulator.
Reason: Resistance of insulators is very low

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true not but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false
D. If both assertion and reason are false.

Explanation

To analyze the given assertion and reason, we will break down the concepts involved step by step.

### Step 1: Understanding the Assertion
The assertion states that if there is a gap between the conduction band and the valence band, electrons in the valence band remain bound, and no free electrons are available in the conduction band, then the material is an insulator.

**Explanation:**
- In semiconductors and insulators, the energy bands are divided into two main categories: the valence band and the conduction band.
- The valence band is filled with electrons, while the conduction band is where free electrons can move and conduct electricity.
- An insulator has a significant energy gap (band gap) between the valence band and the conduction band. This gap prevents electrons from jumping from the valence band to the conduction band, meaning there are no free electrons available for conduction.

### Step 2: Understanding the Reason
The reason states that the resistance of insulators is very low.

**Explanation:**
- This statement is incorrect. Insulators have very high resistance because they do not have free electrons available to conduct electricity. The lack of free charge carriers leads to high resistance, making it difficult for electric current to flow through the material.

### Step 3: Conclusion
Based on the analysis:
- The assertion is **true**: The presence of a gap between the conduction and valence bands does mean that the material is an insulator.
- The reason is **false**: Insulators have high resistance, not low resistance.

### Final Answer
The correct conclusion is that the assertion is true, but the reason is false.