`pK_(a1) , pK_(a_(2))` and `pK_(a_(3))` of `H_(3)PO_(4)` are respectively x,y and z. pH of 0.1 M `Na_(2)HPO_(4)` solution is

Options

A. 1
B. `(1)/(2)(x+y)`
C. `(1)/(2)(y+z)`
D. `(1)/(2) (x+y+z)`

Answer

C

Explanation

`HPO_(4)^(2-)` is amphiprotic
`HPO_(4)^(2-)+H_(2)O hArr PO_(4)^(3-)+H_(3)O^(+)`
`HPO_(4)^(2-) +H_(2)O hArr H_(2)PO_(4)^(-) +OH^(-)`
`:. pH =(pK_(a2)+pK_(a3))/(2)=(1)/(2)(y+z)`
`HPO_(4)^(2-)`