Answer:
O CaCl₂
Explanation:
The compound most likely to contain an ionic bond is CaCl₂ because it is the only specie with a metal and non-metal. 
The metal here is Ca and non-metal is Cl. 
- In this bond type, there is a transfer of electrons from the metal to the non-metal. 
- There must be a significant electronegativity difference between the two bodies for this bond to form. 
- The metal Calcium loses two electrons and becomes isoelectronic with argon. 
- Two chlorine non-metal gain one of the electrons each and becomes stable. 
- The electrostatic attraction between the oppositely charged ions results in the ionic bonding.