Calculate the concentration of nitrate ions, NO3- , in mol dm-3, of a solution made by dissolving 2.5000 g of ferric nitrate nonahydrate in water to give 2.000 L of solution.

Answer 1

You must mean monohydrate.
moles = 2.50g/molar mass Fe(NO3)3.H2O
M = moles/L soln.