Assertion: When a dielectric material is kept inside some external electric field then the net electric field intensity inside the volume of dielectric is always less than external electric field intensity.
Reason: In a normal state, polar molecules of dielectric material are randomly oriented and their net electric field remains zero. If we apply electric field on a dielectric material then the polar molecules experience torque and gets aligned along its direction.

Options

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

Answer

To solve the problem, we need to analyze the assertion and reason provided in the question step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion:**
- The assertion states that when a dielectric material is placed in an external electric field, the net electric field intensity inside the dielectric is always less than the external electric field intensity.
- This is true because the dielectric material responds to the external electric field by polarizing, which reduces the effective electric field inside it.

2. **Understanding the Reason:**
- The reason given explains that in the normal state, the polar molecules in the dielectric are randomly oriented, resulting in a net electric field of zero.
- When an external electric field is applied, these polar molecules experience a torque that aligns them along the direction of the external field.

3. **Analyzing the Normal State:**
- In the absence of an external electric field, the dipoles (polar molecules) in the dielectric are randomly oriented, leading to a net electric field of zero.
- This means that the contributions of the dipoles cancel each other out.

4. **Effect of External Electric Field:**
- When an external electric field is applied, the dipoles align themselves with the field due to the torque experienced by them.
- This alignment creates a polarization effect, where the negative charges of the dipoles move slightly in the opposite direction of the electric field, and the positive charges move in the direction of the field.

5. **Induced Electric Field:**
- The alignment of dipoles creates an induced electric field within the dielectric, which opposes the external electric field.
- The net electric field inside the dielectric can be expressed as:
\[ E_{\text{net}} = E_{\text{external}} - E_{\text{induced}} \]
- Since the induced electric field is always less than the external electric field, it follows that:
\[ E_{\text{net}} < E_{\text{external}} \]

6. **Conclusion:**
- Therefore, both the assertion and the reason are correct. The assertion is supported by the reasoning provided, and they are related as the reason explains why the assertion holds true.

### Final Answer:
- The assertion is true, and the reason is true, and the reason correctly explains the assertion.