UPSC NDA 2 2021 General Ability Solved Paper

N negative is not iso-electronic with
F−because Isoelectronic species are known as atoms or ions that have the same number of electrons.
In isoelectronic species, there the number of electrons would be equal but the elements would be different. In other words, ions and atoms which are having equal numbers of electrons are called the isoelectronic species.