By usual analysis, 1.00 g of compound $(\mathrm{X})$ gave 1.79 g of magnesium pyrophosphate. The percentage of phosphorus in compound $(\mathrm{X})$ is: (nearest integer)\\ (Given, molar mass in $\mathrm{g} \mathrm{mol}^{-1}: \mathrm{O}=16, \mathrm{Mg}=24$, $\mathrm{P}=31$ )