Among the compounds NaCl, KCl, RbCl and CsCl , the one with greatest ionic character is

The favorable conditions to form an ionic bond between the atoms of elements are:

 1.The size of cation should be large and more electropositive.

2. The size of anion should be small and high electron affinity.

3. Both cation and anion must have stable inert gas configuration.

Here, for the given all compounds, CsCl is most ionic character because the cation size is large Cs+ than the remaining cations. The anion (Cl− )is same in all compounds.