Electron pair repulsions in a molecule help in predicting the bond angle because of the Valence Shell Electron Pair Repulsion VSEPR theory. According to this theory, electron pairs both bonding and non-bonding around a central atom in a molecule repel each other and try to stay as far apart as possible to minimize the repulsive forces. This arrangement determines the geometry and bond angles of the molecule.Let's take the example of water H2O to illustrate this concept. In a water molecule, the central atom is oxygen, which has two lone pairs of electrons and two bonding pairs of electrons one with each hydrogen atom . According to the VSEPR theory, these four electron pairs will arrange themselves in a tetrahedral geometry to minimize repulsion. However, since we are only considering the bond angle between the two hydrogen atoms, we will focus on the two bonding pairs.In a perfect tetrahedral geometry, the bond angle between any two bonding pairs is 109.5 degrees. However, in the case of water, the lone pairs of electrons on the oxygen atom repel the bonding pairs more strongly than the bonding pairs repel each other. This is because lone pairs occupy more space and have a higher electron density. As a result, the bond angle between the two hydrogen atoms in a water molecule is slightly reduced to approximately 104.5 degrees.So, using the concept of electron pair repulsion and the VSEPR theory, we can predict that the bond angle in a water molecule is approximately 104.5 degrees.