Which if the following compounds contains one or more covalent bonds? CO2 KCl Na2O CaCl2 CaS?

CO₂ (O=C=O): a molecular compound containing 2 C=O double bonds in each molecule
KCl: an ionic compound containing K⁺ and Cl⁻ ions.
Na₂O: an ionic compound containing Na⁺ and O²⁻ ions.
CaCl₂: an ionic compound containing Ca²⁺ and Cl⁻ ions.
CaS: an ionic compound containing Ca²⁺ and S²⁻ ions.

The answer: CO₂

All chemical bonds have some covalent character. There are no bonds which are 100% ionic. What you want to ask is, "Which compound has bonds with the greatest covalent character?"

The answer to that question is CO2. C-O bonds have about 18% ionic character. The remaining compounds in your question are all salts (CO2 is not a salt) and have bonds with significantly greater ionic character.

It's also important to understand that the oxidation states of the elements in a compound are assigned numbers and are not the actual charges on the elements in the compound.

Answer is CO2, carbon dioxide;

Look at the following video:

https://www.youtube.com/watch?v=dD0Xl4acUFg

B