N=mass /Mr = 9.794/392.16 = 0.0249745
C=m/vx1000 = 0.0249745 x1000 / 250 = 0.099898 therefore = 0.1
Please, be consistent. First, you calculated some N, then, in the next formula, you used some m. It is not easy to followe, you know.
At least your concentration is OK (almost - I would put it as 0.0999).
Now, if concentration of Fe(NH4
O is 0.1, what is concentration of Fe2+
? Before you will start to multiply/divide anything by anything, just think - how many moles Fe2+
per mole of Fe(NH4