Answer:
LiCl.
Explanation:
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In this case, since it is known that the ionic compounds are specially formed between metals and nonmetals, it is possible for us to discard CO and PCl5 as they have both nonmetals.
On the other hand, since the bonds between nonmetals and transition metals like iron and copper may not be completely ionic due to the electronegativity trend, we infer that the most likely ionic compound is LiCl because of the large electronegativity difference.
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