Final answer:
The common exception for naming in this case is option D) MgCl₂, which represents magnesium chloride with two chloride ions balancing the charge on the one magnesium ion.
Step-by-step explanation:
The common exception for naming in this case is option D) MgCl₂. When naming ionic compounds, the name of the cation (metal) is written first, followed by the name of the anion (nonmetal), without the word 'ion'.
In this case, MgCl₂ represents magnesium chloride. The 2 subscript indicates that there are two chloride ions to balance the charge on the one magnesium ion.
The other options, NaCl, CuCl, and CsCl, follow the usual naming convention and do not fall under the category of common exceptions.