what is the formula for the compound with the name manganese(iv) sulfide?
To get a neutral formula out of that we must have one Mn to two S, i.e. MnS2. If you use the “criss-cross method” of finding formulas of binary compounds (in which you put the absolute value of each atom's charge as the subscript of the other atom), you get Mn2S4, which “reduces” (like a fraction) to MnS2.