It should be kept in mind that coefficient ‘3’ will be written as 3BaSO4and not as (BaSO4)3. please explain why ?
According to the IUPAC system of nomenclature of compounds, the number of molecules of a compound shall be represented by a whole number before writing the symbol of the molecule i.e 3BaSO4.
If there are more than one repeating functional groups attached to one metal atom then they are represented by subscript after the functional group. e,g, Cu(NO3)2 i.e two NO3 groups are represented by subscript.
Incase of polyatomic molecules, subscript is used i.e. O2 and not 2O