Question

how to calculate number of ions in a compound

Answer 1

let's take an example of Trisodium phosphate

Write the ionic formula

Na3PO4 which is (Na+)3PO43-

So in each formula unit there are 3 sodium ions and 1 phosphate ion
In 100 formula units, there are 300 sodium ions and 100 phosphate ions.

So in 1 mole of sodium phosphate, there will be 3 mole of sodium ions and 1 mole of phosphate ions
3 mole of sodium ions = 3 x 6.02 x1023 ions and 1 mole of phosphate ions = 6.02 x1023 ions

So work out how many ions there will be in 2 moles of sodium phosphate.