Answer:

Dipole Moment:
The dipole moment is a measure of the polarity of a molecule. It is defined as the product of the magnitude of the charge on either end of the bond and the distance between them. In the case of a heteronuclear molecule like HF, the shared electron pair between the two atoms gets displaced more towards fluorine due to its higher electronegativity. This results in a partial positive charge on the hydrogen atom and a partial negative charge on the fluorine atom, creating a dipole moment.

Explanation:
- In a covalent bond, the electrons are shared between the two atoms. However, the electrons are not always shared equally due to the difference in electronegativity of the atoms involved.
- Electronegativity is a measure of the tendency of an atom to attract electrons towards itself in a chemical bond.
- In the case of HF, fluorine has a higher electronegativity compared to hydrogen. Fluorine is the most electronegative element in the periodic table.
- Due to the higher electronegativity of fluorine, it attracts the shared electron pair in the HF molecule more strongly towards itself.
- This results in a partial negative charge on the fluorine atom and a partial positive charge on the hydrogen atom.
- The separation of charge creates a dipole moment in the HF molecule, with the positive end towards the hydrogen atom and the negative end towards the fluorine atom.
- The dipole moment is a vector quantity and is represented by an arrow pointing towards the negative end of the molecule.
- The dipole moment of HF is significant due to the large electronegativity difference between hydrogen and fluorine.
- This dipole moment makes HF a polar molecule, with one end being more positive (hydrogen) and the other end being more negative (fluorine).

Conclusion:
The correct answer is option 'A' - dipole moment. The displacement of the shared electron pair towards fluorine, due to its higher electronegativity, creates a dipole moment in the HF molecule.