Strontium Sr is an alkaline earth metal with an electronegativity of 0.95, while Oxygen O is a non-metal with an electronegativity of 3.44. The difference in electronegativity between Sr and O is 3.44 - 0.95 = 2.49. In general, when the electronegativity difference between two elements is greater than 1.7, the bond formed is considered ionic. In this case, the electronegativity difference is 2.49, which is greater than 1.7. Therefore, the inorganic solid formed between Strontium Sr and Oxygen O is an ionic solid. The compound formed is Strontium oxide SrO .