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

### Step 1: Understanding Polar Molecules
- **Definition**: Polar molecules are molecules that have a permanent dipole moment due to the unequal distribution of electron density.
- **Example**: Water (H₂O) is a common example of a polar molecule where the oxygen atom is more electronegative than the hydrogen atoms, creating a dipole.

**Hint**: Recall that a dipole moment arises when there is a separation of positive and negative charges in a molecule.

### Step 2: Permanent Dipole Moment
- **Permanent Dipole Moment**: This is a measure of the separation of positive and negative charges in a molecule. In polar molecules, this dipole moment is always present, even in the absence of an external electric field.
- **Reason for Permanent Dipole**: The centers of positive and negative charges do not coincide; they are separated by a distance, leading to a permanent dipole moment.

**Hint**: Think about how the shape and electronegativity of atoms in a molecule contribute to the dipole moment.

### Step 3: Analyzing the Assertion
- **Assertion**: "Polar molecules have permanent dipole moment."
- **Evaluation**: This statement is true because polar molecules, by definition, have a permanent dipole moment due to the separation of charges.

**Hint**: Confirm that the definition of polar molecules aligns with the assertion.

### Step 4: Analyzing the Reason
- **Reason**: "In polar molecules, the centers of positive and negative charges coincide even when there is no external field."
- **Evaluation**: This statement is false. In polar molecules, the centers of positive and negative charges do not coincide; they are separated by a distance, which is what gives rise to the dipole moment.

**Hint**: Consider the implications of charge separation in determining the dipole moment.

### Step 5: Conclusion
- **Final Evaluation**:
- The assertion is true: Polar molecules do have a permanent dipole moment.
- The reason is false: The centers of positive and negative charges do not coincide; they are separated.

Thus, the correct conclusion is that the assertion is true, but the reason is false.

### Summary
- **Assertion**: True
- **Reason**: False

**Final Answer**: The assertion is true, and the reason is false.