The number of Fe(ii) ions that are in 10.0g of FeSO4 is 3.961 x10^22 ions
calculation
find the number of moles of FeSO4 = mass/molar mass
= 10g / 151.9 g/mol=0.0658 moles since there 1 atom of fe the moles of Fe= 0.0658 moles
by use of Avogadro's constant
that is 1 mole= 6.02 x10^23 ions
0.0658moles=? ions
= 0.0658 mole x(6.02 x10^23)] / 1 mole = 3.961 x10^22 ions