Answer:
BaSO₄
Explanation:
It is possible to know if a bond is ionic or covalent using the electronegativity of the atoms in the bond. If electronegativity difference is higher than 1.8, the bond is ionic, if doesn't, bond is covalent.
CaI₂ has the Ca-I bond where electronegativity of Ca and I are 1 and 2.66. Difference of electronegativity is 1.66 → <em>Bond is covalent.</em>
COS has the C-O and C-S bonds where electronegativity of C, O and S are 2.55, 3.44 and 2.55. Difference of electronegativity are 0.89 and 0 → <em>Bonds are covalent.</em>
BaSO₄ has the Ba-O and O-S bonds where electronegativity of Ba, O and S are 0.89, 3.44 and 2.55. Difference of electronegativity are 2.55 and 0.89 → <em>Bonds are ionic and covalent respectively</em><em>.</em>
SF₆ has the S-F bond where electronegativity of S and F are 2.55 and 3.98. Difference of electronegativity is 1.43 → <em>Bond is covalent.</em>