Answer
In each case, the total positive and total negative charge of the compounds must cancel. Therefore the compounds with the cations X^+, X^2+ and X^5+, combined with the SO4^2 anion are X2 SO4, X SO4 and X2 (SO4)5 respectively.
Work Step by Step
Recognize the fact that whenever a cation can have multiple oxidation states (1+,2+ and 5+ in this case), the name of the compound must indicate the charge. Therefore the names of the compounds in part a must be exy(I)sulfate, exy(II)sulphate and exy(V)sulphate
