Final answer:
The covalent bonding model best describes SCl₂, as it involves the sharing of electrons between non-metal atoms, sulfur and chlorine.
Step-by-step explanation:
The covalent bonding model is most useful in describing SCl₂ among the options given. This is because covalent bonding involves the sharing of electrons between two non-metal atoms. Sulfur and chlorine are both non-metals, therefore they will share electrons and form a covalent bond. In contrast, MgCl₂, CoCl₂, and NiCl₂ involve metals and non-metals, typically indicative of ionic bonding where electrons are transferred from the metal to the non-metal, forming cations and anions.