Find charge on 1.90 g of PO4 2-

The molecular mass of PO₄^2- 95 g.

The no of electrons in  PO₄^2- are  49.

Charge on one electron =1.6 x10^-19 C

Number of molecules in 1.9 g PO₄^2-  = 6.02 X10^{23  X}   1.9

                                                       ------------------

                                                            95

                                                                     ⁼ 0.1204 X 10²³

So number of electrons in 0.1204 X 10²³ molecules are 0.1204 X 10²³  x 49 =5.8996 X 10²³ electrons.

 So charge = 5.8996 X 10²³ X 1.6 x10^-19

 

                     ^{=9.43936 X 104}