what is inter-electronic repulsion ?
Inter electronic repulsion as the name indicates repulsion between electrons. This take place in atoms, where electrons are present within the same shell or in different shell. This also take place when two electrons are present within the same orbital because of which hund’s rule is obeyed.
If atom is smaller in size and more electrons are present in valence shell, they would must cause repulsion like in F atom.
You know that the electrons are negatively charged. You also might have studied that these electrons revolve around the nucleus in definite paths called orbits. So, they tend to repel each other due to similar nature and magnitude of charges. This is what is known as inter electronic repulsion.