Which of the following pairs of elements would most likely form a salt?

O and N

Ca and Mg

Cl and Li

H and He

A salt is an ionic compound which needs a positive charge ion and a negative ion charge to form a salt. This means that the pair of element should be a metal and non-metal. This is simply because metal atoms tend to lose negative charge electrons and form positive ions while non-metals tend to receive the electrons from the metal atom to form negative charge ions. So answer is Cl and Li.