Potassium iodide (KI) forms an ionic bond. Potassium and iodine have very different electronegativities. The two atoms would form an ionic bond since ionic bonds form between atoms with a large difference in electronegativity (difference>1.7 using the Pauling scale will result in an ionic bond). 

Ionic bonds are bonds in which there is a complete transfer of electrons between two elements. They are formed between two elements with a large difference in electronegativity, like a metal and nonmetal. Molecules with similar electronegativities share their electrons and form covalent bonds.

Because bromine has a much higher electronegativity than potassium, it will fully take an electron from potassium to form a complete octet, leaving potassium also with a complete octet.

, , and all form covalent bonds and share electrons between the atoms of the molecule.

The degree of ionic character of a compound is determined by comparing the electronegativities of the species involved. The greater the difference in electronegativity, the more ionic the compound.

Here the greatest arithmetic difference is found in yttrium trichloride.

The compound  contains a metal (potassium) and a nonmetal (oxygen), so it is an ionic compound, with no transition metals. To name an ionic compound, the following rules apply:

- the metal component's name does not change, regardless of quanitiy or charge

- the non-metal component's name ends in -ide, and has no prefix 

- if the metal is a transition metal, the metal's charge is specified with a Roman numeral

Using these rules, the correct name is potassium oxide.

An ionic bond is an electrostatic force between a positively charged cation (formed when electrons are lost) and a negatively charged anion (formed when electrons are gained). While one answer choice mentions positive and negative, it is actually a description of a polar covalent bond. The easiest way to recognize this is the fact that it specifies a bond between two nonmetals. A metal in generally a component of an ionic compound.

Ionic compounds are made of atoms that are held together by ionic bonds. These bonds allow charged particles that have very different electronegativities to stick together, forming 3D crystals. For example, potassium and bromine form potassium bromide, an anti-convulsant. The electrons are shared very disproportionately between the positive and negatively charged particles, with the all the electrons located on the more electronegative atom. Ionic compounds are not non-polar because non-polar is used to describe a molecule whereas ionic compounds are not molecules. Water is an example of a polar molecule but is not an ionic compound since The hydrogens and oxygen share their electrons.