Final answer:
Sodium fluoride (NaF) is an ionic compound formed by the transfer of electrons from sodium to fluorine, resulting in a crystal lattice structure.
Step-by-step explanation:
The compound sodium fluoride (NaF) is best described as an ionic compound. This is because it is formed from the transfer of electrons between a metal (sodium, Na) and a nonmetal (fluorine, F). As we can see from provided information, when sodium and fluorine combine, sodium loses an electron, becoming a positively charged ion (Na+), while fluorine gains that electron, becoming a negatively charged ion (F−). The resulting electrostatic attraction between the oppositely charged ions is what forms the ionic bond between them, resulting in the formation of NaF. This compound typically exists in a regular, three-dimensional lattice structure known as a crystal, rather than discrete molecules. Therefore, the correct answer to the question is 'b. Ionic; transfer of electrons'.