Question

How many moles of magnesium phosphate will contain 0.25 moles of oxygen atoms ?

Answer 1

Magnesium phosphate (Mg₃(PO₄)₂)

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8 moles of oxygen atoms are present in 1 mole of magnesium phosphate.

So, 0.25 moles of oxygen atoms will be present in = $\frac{1}{8}\times 0.25=0.03125\mathrm{mol}\mathrm{of}\mathrm{magnesium}\mathrm{phosphate}$