0.5 g of an organic substance containing phosphorus was heated with conc `HNO_(3)` in the carius tube, the phosphoric acid thus formed was precipitated with magnesia mixture `(MgNH_(4)PO_(4))` which on ignition gave a residue to 1.0 g of megnesium pyrophosphate `(Mg_(2)P_(2)O_(7))` The percentage of phosphorous in the organic compound is

Options

A. `55.85%`
B. `29.72%`
C. 19.81%`
D. `20.5%`

Answer

A

Explanation

Mw of `Mg_(2)P_(2)O_(7)=(24xx21+31xx2+16xx7)=222`
`therefore % of P=(62)/(222)xx("weight of Mg_(2)P_(2)O_(7))/("weight of compound")xx100`
`=(62)/(222)xx(1.0)/(0.5)xx100=55.85%`