How many moles of magnesium phosphate will contain 0.25 moles of oxygen atoms
8 moles oxygen ———→ 1 mol of Mg3(PO4)2
1 mol of O ———→ 1/8 mol of Mg3(PO4)2
0.25 mol of Oxygen ——→ 1/8 x 25/100 mol of Mg3(PO4)2
………………………………….. => 1/32 mol of Mg3(PO4)2
………………………………….. => 0.03125 M of Mg3(PO4)2
…………………………………. => 3.125 x 10^(-2)