Final answer:
The ionic compound that requires a roman numeral in its name to indicate the charge is D. CuSO4, which is named copper(II) sulfate.
Step-by-step explanation:
Among the choices given, the ionic compound that would need a roman numeral to show its charge when writing the name of it is D. CuSO4. This is because copper (Cu) can have more than one possible charge, unlike the other metals listed such as lithium (Li), magnesium (Mg), or nitrogen (in the ammonium ion NH4+) which have fixed charges. The correct way to name CuSO4 would be copper(II) sulfate, where the roman numeral II represents the +2 charge of the copper ion.