Which formula represents an ionic compound?

a. NaCl

b. N2O

c. HCl

d. H2O

An ionic compound is held my oppositely charged atoms. Therefore, this would mean that one is a positive and another is a negative held together.

The compound that best fits this description is NaCl. That is because the Na (Sodium) would be positively charged because it lost electrons, and Cl (Chlorine) would be negatively charged because it gained electrons.

Our final answer: a. NaCl