Assertion: In the absence of an external electric field, the dipole moment per unit volume of a polar dicletric is zero.
Reason : The dipoles of a polar diclectric are randomaly oriented.

Options

A. If both assertion and reason are ture and reason is the correct explanation of assertion.
B. If both assertin and reason are ture 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 solve the question, we need to analyze both the assertion and the reason provided.

### Step 1: Understand the Assertion
The assertion states that "In the absence of an external electric field, the dipole moment per unit volume of a polar dielectric is zero."

### Step 2: Analyze the Reason
The reason given is that "The dipoles of a polar dielectric are randomly oriented."

### Step 3: Relate the Assertion and Reason
In polar dielectrics, the molecules possess permanent dipole moments. However, in the absence of an external electric field, these dipoles are oriented randomly. Because of this random orientation, the individual dipole moments cancel each other out, leading to a net dipole moment of zero per unit volume.

### Step 4: Conclusion
Since the assertion correctly states that the dipole moment per unit volume is zero when there is no external electric field, and the reason correctly explains why this is the case (due to random orientation of dipoles), we conclude that both the assertion and the reason are true. Furthermore, the reason is a correct explanation of the assertion.

### Final Answer
- **Assertion**: True
- **Reason**: True (and it correctly explains the assertion)

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