(C) KBr
An ionic compound is made up of a metal and a nonmetal. K is a metal while bromine is a nonmetal. Thus K transfers its one electron to bromine in order to form an ionic compound.
An ionic compound is composed of ions, a positive ion i.e. a cation and a negative ion i.e. an anion. The bond formed between the two elements is an ionic bond which is formed by the complete transfer of electrons from an electropositive element to the electronegative element. The electropositive element loses its electron and gains a positive charge whereas the electronegative atom accepts that electron and gains a negative charge.
In the given examples:
KBr is made up of ions
Potassium being electropositive becomes positively charged K+
Bromine is electronegative and becomes negatively charged Br-
KBr = K⁺Br⁻
