Question

when a formula unit of magnesium sulfide, mgs, is separated into magnesium and sulfur particles, the particles are called
a. molecules.
b. ions.
c. isotopes.
d. compounds.

Explanation:

Magnesium sulfide (MgS) is an ionic compound formed from positively charged magnesium ions ($\text{Mg}^{2+}$) and negatively charged sulfide ions ($\text{S}^{2-}$). When separated into its constituent charged particles, these particles are defined as ions. Molecules are neutral covalent particles, isotopes are variants of the same element, and compounds are pure substances made of multiple elements, so these do not fit.

Answer:

C. ions.