How do you determine if a compound is ionic, acid, or covalent ?

Question

I.E. silicon dioxide

Answer 1

SiO2 is a covalent compound (the electronegativity of Si is 1.9 and that of oxygen is 3.0, the difference is less than 1.9 so it is classified as covalent. It isn't soluble in water; therefore, its acidity or basicity is not known. The statement doesn't make sense with the word acid in it.