Oxygen is more electronegative than nitrogen so it attracts the bonding electrons to a greater extent

Nd in water there are 2 lone pairs nd in ammonia it's just a one lone pair nd lone - lone repulsion are more than bond pair - bond pair repulsion so hence in water charge separtion gets to be more than ammonia due to more lp - lp than in ammonia so water has more dipole moment than ammonia cause dipole is product of charge nd the distance which is charge separation !!!

Introduction:
The dipole moment is a measure of the polarity of a molecule. It is defined as the product of the charge (Q) and the distance (d) between the charges in a molecule. A dipole moment occurs when there is a separation of positive and negative charges in a molecule. In this case, we are comparing the dipole moments of water (H2O) and ammonia (NH3).

Dipole Moment of Water (H2O):
Water is a polar molecule due to its bent molecular geometry and the electronegativity difference between oxygen and hydrogen atoms. The oxygen atom is more electronegative than the hydrogen atoms, resulting in a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms. This separation of charges creates a dipole moment in the molecule.

Dipole Moment of Ammonia (NH3):
Similarly, ammonia is also a polar molecule due to its pyramidal molecular geometry and the electronegativity difference between nitrogen and hydrogen atoms. The nitrogen atom is more electronegative than the hydrogen atoms, leading to a partial negative charge on the nitrogen atom and partial positive charges on the hydrogen atoms. This separation of charges creates a dipole moment in the molecule.

Comparison of Dipole Moments:
The dipole moment of a molecule is influenced by two factors: the magnitude of the charge separation and the distance between the charges.

Charge Separation:
In water (H2O), the electronegativity difference between oxygen and hydrogen atoms is higher than the electronegativity difference between nitrogen and hydrogen atoms in ammonia (NH3). This greater electronegativity difference in water leads to a greater charge separation, resulting in a larger dipole moment compared to ammonia.

Distance between Charges:
The dipole moment is also affected by the distance between the charges. In water, the oxygen atom is more electronegative, causing the electron density to be pulled closer to the oxygen atom. This results in a shorter distance between the positive and negative charges, further enhancing the dipole moment. In ammonia, the nitrogen atom is less electronegative than oxygen, resulting in a larger distance between the charges and a smaller dipole moment compared to water.

Conclusion:
In conclusion, the dipole moment of water (H2O) is greater than that of ammonia (NH3) due to the higher electronegativity difference and shorter distance between charges in water. The dipole moment is an important property to consider in various chemical reactions and physical interactions involving polar molecules.