An ionic compound is formed when there is a reaction between the elements

a) strontium and chlorine

b) hydrogen and chlorine

c) nitrogen and oxygen

d) sulfur and oxygen

In order for an ionic compound to be created, there has to be a reaction between a metal and a non-metal. Having this in mind, the correct answer is A. strontium and chlorine. Strontium (Sr) is an alkaline earth metal, whereas chlorine (Cl) is a halogen gas, so a non-metal. There is no this type of a combination of metal + non-metal in other options, so only A is correct.