Molarity help/solubility

A 250mL aqueous solution contains 1.75g of (NH4)2SO4. Which of the following statements about this solution is correct?

Ok so i got it down to 2 options

The concentration of SO4^2- is 5.30e-2 M
The concentration of NH4+ is 5.30e-2 M

the answer is The concentration of SO4^2- is 5.30e-2 M

but why is it SO4^2- ??

think about it this way. When you drop the ammonium sulfate into water it will dissociate into two different ions: ammonium (NH4) and sulfate (SO4). You have though two molecules of NH4 for every 1 SO4. So when calculating concentrations you have to multiply NH4 by 2. Therefore

1.75 g * 1 mol/132.14 g = .01324 mols
molarity = mols/liters
250 mL = .250 L
.01324 mols/.250 L = .530 e -2 M

for NH4 you have
1.75 g * 2 mol/132.14 g = .02649 mols
.02649/.250 L =1.06 e -1

Because the concentration of NH4^+1 will be 2 x the concentration of SO4^-1
(NH4)2SO4
2 NH4^+1 and 1 SO4^-2