A.large electronegativity differences
Ionic bonds are a type of chemical bond that forms between two atoms when one atom donates an electron to the other atom. This results in the formation of ions, which are atoms or molecules that have a net charge due to the loss or gain of electrons. Ionic bonds typically form between atoms that have large differences in electronegativity, which is a measure of an atom's ability to attract electrons. This is because atoms with large differences in electronegativity tend to have a strong tendency to transfer electrons from one atom to the other, resulting in the formation of ions and ionic bonds.