The answer is B. A mixture can be separated as shown in the example.<span />
It would be MnSO4
The (II) lets you know it’s the form with a 2+ charge and Sulfate has a 2- charge
These will cancel out making it plain MnSO4
If it was manganese (iii) sulfide the answer would be Mn2(SO4)3
Aluminum chloride - It does not have the prefix "tri-" since it is ionic. The other compounds listed in the question are covalent and require prefixes.