Valency of Y is +1 (since it is monovalent )
and valency of sulphate (SO42-) is = 2
Using the method of cross multiplication,
Y SO4
1 2
Thus compound formed by Y and sulphate group would be : Y2(SO4)
Similarly valency of phosphate (PO43-) is = 3
Using the method of cross multiplication,
Y PO4
1 3
Thus compound formed by Y and phosphate group would be : Y3(PO4)