Assertion: Polar mlecules have permanent dipole moment.
Reason : In polar molecule, the centres of positive and negative charges coincide evcen wehen there is no external field.

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-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "Polar molecules have a permanent dipole moment."
- This is true because polar molecules have an uneven distribution of electron density, leading to a separation of charges (positive and negative) within the molecule. This results in a permanent dipole moment.

2. **Understanding the Reason**:
- The reason states that "In polar molecules, the centers of positive and negative charges coincide even when there is no external field."
- This statement is false. In polar molecules, the centers of positive and negative charges do not coincide; instead, they are separated. This separation is what gives rise to the permanent dipole moment. The positive and negative charges are not aligned or coinciding, even in the absence of an external electric field.

3. **Analyzing the Relationship**:
- Since the assertion is true (polar molecules do have a permanent dipole moment), but the reason is false (the centers of positive and negative charges do not coincide), we conclude that the assertion stands independently of the reason.

4. **Choosing the Correct Option**:
- Based on the analysis, we find that the correct option is: "Assertion is true but reason is false."

### Final Answer:
The correct option is **Option 3**: Assertion is true but reason is false.

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