Assertion : All diatomic molecules with polar bond have dipole moment.
Reason : Dipole moment is a vector quantity.

Options

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

Answer

To analyze the assertion and reason provided in the question, we can break it down into a step-by-step solution.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "All diatomic molecules with polar bond have dipole moment."
- A polar bond occurs when there is a significant difference in electronegativity between the two atoms in the bond. This results in one atom having a partial negative charge and the other having a partial positive charge.

2. **Example of a Diatomic Molecule**:
- Consider the diatomic molecule HCl (hydrochloric acid). In HCl, chlorine (Cl) is more electronegative than hydrogen (H).
- This difference in electronegativity creates a polar bond, with Cl carrying a partial negative charge (δ-) and H carrying a partial positive charge (δ+).

3. **Dipole Moment**:
- The dipole moment is a measure of the separation of positive and negative charges in a molecule. It is a vector quantity, which means it has both magnitude and direction.
- In the case of HCl, the dipole moment points from H (less electronegative) to Cl (more electronegative), indicating the direction of the charge separation.

4. **Conclusion on Assertion**:
- Since all diatomic molecules with polar bonds (like HCl) have a dipole moment due to the difference in electronegativity, the assertion is **true**.

5. **Understanding the Reason**:
- The reason states that "Dipole moment is a vector quantity."
- This is indeed correct; dipole moments are represented as vectors because they have both direction and magnitude.

6. **Relation Between Assertion and Reason**:
- While both the assertion and reason are true, the reason does not correctly explain why all diatomic molecules with polar bonds have a dipole moment. The dipole moment arises due to the difference in electronegativity, not solely because it is a vector quantity.

7. **Final Evaluation**:
- Therefore, the assertion is true, the reason is true, but the reason does not provide the correct explanation for the assertion. Thus, the correct option is that both statements are true, but the reason is not a correct explanation for the assertion.

### Final Answer:
- Assertion: True
- Reason: True
- Correct Option: Both are true, but the reason is not the correct explanation for the assertion.